COLLEGE  OF  AGRICULTURE 
DAVIS,  CALIFORNIA 


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METALLURGICAL 

ANALYSIS 


BY 

NATHANIEL  WRIGHT  LORD,  E.  M. 

LATE  PROFESSOR  OF  METALLURGY  AND  MINERALOGY,  OHIO  STATE  UNIVERSITY 

AND 

DANA  J.  DEMOREST,  B.  Sc.  in  Chem.  Eng. 

PROFESSOR  OF  METALLURGY,  OHIO  STATE  UNIVERSITY 


FOURTH  EDITION 
REVISED,  ENLARGED  AND  RESET 


THIRD  IMPRESSION 
UNIVERSITY  OF  CALIFORNIA 

LIBRARY 

COLLEGE  OF  AGRICULTURE 
DAVIS 


McGRAW-HILL  BOOK  COMPANY,  INC, 
239  WEST  39TH  STREET.     NEW  YORK 


LONDON:  HILL  PUBLISHING  CO.,  LTD. 

0  &  8  BOUVERIE  ST.,  E.  C. 

1916 


COPYRIGHT,  1903,  BY 
NATHANIEL  WRIGHT  LORD 


COPYRIGHT,  1913  AND  1916,  BY  THE 
MCGRAW-HILL  BOOK  COMPANY,  INC. 


THE    MA.IT.K     PRESS     YORK    J»A 


PREFACE  TO  THE  FOURTH  EDITION 

The  fourth  edition  of  this  book  contains  about  ten  pages  more 
than  the  third  edition.  This  additional  matter  consists  largely 
of  amplification  of  methods  presented  in  the  previous  edition. 

At  the  same  time  advantage  was  taken  of  the  opportunity  to 
correct  errors  discovered  in  the  third  edition,  to  eliminate  some 
ambiguities  of  expression  and  make  changes  in  the  arrangement, 
with  a  view  to  securing  a  greater  degree  of  uniformity  in  the 
presentation  of  the  methods. 

D.  J.  DEMOREST. 

February,  1916. 


PREFACE  TO   THE   FIRST  EDITION 

These  notes  were  written  for  the  use  of  the  writer's  students 
in  the  metallurgical  laboratory  of  the  Ohio  State  University. 

The  object  was  to  give  in  a  condensed  form  the  series  of  se- 
lected methods  in  metallurgical  analysis  which  made  up  the 
course  of  study. 

To  the  descriptions  of  the  processes,  such  explanations  have 
been  added  as  experience  has  shown  to  be  desirable  for  the  assist- 
ance of  the  student  in  understanding  the  conditions  necessary 
for  accurate  results. 

Such  methods  only  are  given  as  have  been  tested  by  repeated 
use  in  the  laboratory  and  found  satisfactory. 

No  attempt  is  made  to  describe  general  reagents  or  apparatus, 
as  students  prepared  to  take  this  course  are  always  familiar 
with  all  ordinary  laboratory  equipment,  and  for  special  forms  of 
apparatus  reference  is  made  to  easily  accessible  books  and  papers. 

The  writer  wishes  to  acknowledge  his  obligation  to  Blair, 
Troilius  and  other  standard  writers,  as  well  as  to  numerous 
papers  in  the  various  technical  and  scientific  journals,  though  it 
has  been  impossible  to  give  credit  in  detail  to  all  the  sources 
from  which  material  was  taken  in  compiling  these  notes. 

The  references  added  are  only  those  which  it  seemed  impor- 
tant the  student  should  consult  for  fuller  information  on  the 
subject. 

October  28.  1SM. 


viu 


CONTENTS 

PAGE 

PREFACE v 

INTRODUCTION      xvij 

CHAPTER  I 

THE  SELECTION  AND  PREPARATION  OF  -SAMPLES  FOR  ANALYSIS.    .    .       1 
General  principles — Sampling  of  metals — "Weighing  out"  from 
the     laboratory     sample — Estimation     of     moisture — Sampling 
coal — Sampling   iron   ores — Sampling   pig-iron — Sampling   equip- 
ment. 

CHAPTER  II 

THE  ANALYSIS  OF  LIMESTONES 12 

Process  of  analysis — Notes  on  the  process — The  volumetric 
determination  of  lime — Solution  required — Notes  on  the  process — 
Determination  of  free  lime — N/5  hydrochloric  acid. 

CHAPTER  III 

THE  DETERMINATION  OF  IRON  IN  ORES 22 

The  determination  of  iron  by  potassium  dichromate  after  reduc- 
tion of  the  ferric  chloride  by  stannous  chloride — Preparation  of 
the  solutions — 1.  Potassium  dichromate  solution — 2.  Stannous 
chloride  solution — 3.  Saturated  solution  of  mercuric  chloride — 
4.  A  very  dilute  solution  of  potassium  ferricyanide — Process  for 
the  assay — Notes  on  the  process — The  determination  of  iron  by 
titration  by  potassium  permanganate  after  reduction  by  metallic 
zinc — Solution  required — 1.  Permanganate  solution — Standardiza- 
tion of  the  permanganate — 2.  Titrating  solution — Preparation  of 
the  reductor — Notes  on  the  process — The  Permanganate  method 
with  reduction  by  stannous  chloride — Determination  of  ferrous 
oxide  in  iron  ore. 

CHAPTER  IV 

THE  DETERMINATION  OF  PHOSPHORUS  IN  IRON  ORES,  IRON  AND  STEEL.  %  34 
Determination  of  phosphorus  with  final  weighing  as  magnesium 
pyrophosphate — Process  for  iron  ores — Solutions  required — 1. 
"Magnesia  mixture." — 2.  "Molybdic  acid  solution" — Modifica- 
tion of  the  process  for  ores  containing  titanium — Determination  of 
phosphorus  in  black  band  and  other  ores  which  contain  much 
carbonaceous  matter — Determination  of  phosphorus  in  mill  cinder 
— Determination  of  phosphorus  in  iron  and  steel  by  the  molybdate 

ix 


xii  CONTENTS 

CHAPTER  XI 

PAGE 

THE    DETERMINATION   OF   TUNGSTEN,    CHROMIUM,    AND   SILICON   IN 

STEEL 158 

Gravimetric  method — Notes  on  the  tungsten  and  chromium 
determinations — Volumetric  method  for  tungsten — Colorimetric 
determination  of  chromium  when  present  in  small  amounts — 
Notes  on  the  process. 

CHAPTER  XII 

DETERMINATION  OF  MOLYBDENUM  IN  STEEL 163 

Process  of  analysis — Notes  on  the  process — Qualitative  test  for 
molybdenum. 

CHAPTER  XIII 

THE  DETERMINATION  OF  TITANIUM 166 

Process  of  analysis  (colorimetric) — Gravimetric  method— Notes 
on  the  process — Standard  titanium  solution — Determination  of 
titanium  by  precipitation  from  acid  solution — Process  of  analysis. 

CHAPTER  XIV 
THE  DETERMINATION  OF  COPPER  IN  IRON  AND  STEEL 172 

CHAPTER  XV 

DETERMINATION  OF  ARSENIC  IN  IRON  AND  STEEL 173 

CHAPTER  XVI 

THE  DETERMINATION  OF  ALUMINUM  IN  IRON  AND  STEEL 176 

Stead's  method. 

CHAPTER  XVII 

THE  DETERMINATION  OF  NITROGEN  IN  STEEL 178 

Hydrochloric  acid  of  1:1  specific  gravity,  free  from  ammonia — 
Solution  of  caustic  soda — Nessler's  reagent — Standard  ammonia 
solution — Distilled  water  free  from  ammonia. 

CHAPTER  XVIII 

THE  DETERMINATION  OF  OXYGEN  IN  STEEL 181 

Samples — Apparatus — Method  for  total  oxygen. 

CHAPTER  XIX 

DETERMINATION  OF  HYDROGEN  IN  STEEL  .  .186 


CONTENTS  xiii 

CHAPTER  XX 

PAGE 

THE  DETERMINATION  OF  SPELTER  AND  TIN  PLATE  COATING  ....    189 
Analysis  of  tin  and  terne  plate  and  lead-coated  sheets — Method 
of  the  American  Rolling  Mills  Co. 

CHAPTER   XXI 

THE  DETERMINATION  OF  ZINC  IN  ORES 193 

Process  of  analysis — Standardization  of  the  ferrocyanide — Notes 
on  the  process — Method  of  Von  Schultz  and  Low — The  modified 
Waring  method  for  zinc — Process  of  analysis — Notes. 

CHAPTER  XXII 

THE  DETERMINATION  OF  COPPER  IN  ORES 199 

The  iodide  method  for  copper — Process  for  ores — Standardization 
of  the  thiosulfate  solution — Notes  on  the  process — Short  iodide 
method  for  copper — Process  of  analysis — The  electrolytic  deter- 
mination of  copper  in  ores,  etc. — Method  for  ores  free  from  arsenic, 
antimony  or  bismuth — Method  for  impure  ores — Process  of  analy- 
sis— Notes  on  the  process — The  cyanide  method  for  copper  in  ores 
— Process  of  analysis — Standard  cyanide  solution — Notes  on  the 
process — Sulfocyanate-permanganate  method  for  copper — Process 
of  analysis — Notes  on  process. 

CHAPTER  XXIII 

THE  DETERMINATION  OF  LEAD  IN  ORES 213 

The  electrolytic  determination  of  lead — Process  of  analysis  for 
ores  free  from  arsenic,  antimony  or  bismuth — Method  for  ores 
containing  antimony  or  bismuth — The  volumetric  chromate 
method  for  lead — Solutions  required — Hydrochloric  acid  mixture — 
Potassium  dichromate — Starch  solution — Process  of  analysis — 
Notes  on  the  process — Wilder's  modification — Notes  on  the  method. 

CHAPTER  XXIV 

THE  DETERMINATION  OF  TIN  IN  ORES 219 

CHAPTER  XXV 

THE  ANALYSIS  OF  REFINED  COPPER 222 

Process  of  analysis — Antimony — Bismuth — Selenium  and  tel- 
lurium— Starch  indicator — Iodine  solution — Lead,  iron,  nickel, 
cobalt  and  zinc — Determination  of  gases  in  copper — Sulfur. 

CHAPTER  XXVI 
ANALYSIS  OF  REFINED  LEAD    .  .    .   229 


xiv  CONTENTS 

CHAPTER  XXVII 

PAGE 

THE  ANALYSIS  OF  BEARING  METALS 232 

Process  of  analysis — Antimony — Copper — Tin — Modification 
when  arsenic  is  present. 

CHAPTER  XXVIII 

THE  ANALYSIS  OF  SPELTER      237 

Iron — Cadmium. 

CHAPTER  XXIX 

BRASS  AND  BRONZE  ANALYSIS 240 

Analysis  of  brass — Solder  analysis — Bronze  analysis. 

CHAPTER  XXX 

THE  ANALYSIS  OF  COAL  AND  COKE 242 

Proximate  analysis — Moisture — Volatile  matter — Fixed  carbon — 
Ash — Methods  of  analysis — Weighing  out  a  sample  for  a  deter- 
mination— Moisture — Ash — Volatile  matter — Fixed  carbon — The 
determination  of  sulfur  in  coal — Eschka's  method — Preparation 
of  the  soda-magnesia  mixture  (Eschka  mixture) — Sulfur  in  the 
calorimeter  washings — The  determination  of  phosphorus  in  coal 
and  coke — The  ultimate  analysis  of  coal — The  determination  of 
the  carbon  and  hydrogen  by  combustion  in  oxygen — The  arrange- 
ment of  the  apparatus — Testing  the  apparatus — Process  of  analysis 
— The  determination  of  the  nitrogen  in  coal — The  oxygen  in  coal — 
Testing  a  coal  as  to  the  quality  of  the  coke — The  determination  of 
the  porosity  of  coke — Determination  of  the  specific  gravity  of  the 
coke — The  determination  of  the  volume  or  apparent  specific  gravity 
of  the  coke  in  lumps — Testing  the  effect  of  "washing  "  on  coal — The 
determination  of  the  heating  power  of  coal. 

CHAPTER  XXXI 

THE  ANALYSIS  OF  GASES 264 

The  analysis  of  flue  gas — Sampling  the  gas — Apparatus — Prepa- 
ration of  the  reagents — Potassium  pyrogallate — Ammoniacal  cu- 
prous chloride — Making  the  analysis — Blast  furnace  and  producer 
gas — Apparatus  used — Filling  the  pipettes — Process  of  analy- 
sis— Notes  on  the  process — The  copper  oxide  method — The 
analysis  of  coke-oven  gas — Determination  of  hydrogen  by  com- 
bustion in  contact  with  palladium — The  palladiumized  asbestos — 
Procedure  for  the  determination  of  hydrogen — Determination  of 
the  Methane  (and  Ethane) — Notes  on  the  analysis  of  coke-oven  gas 
— Analysis  of  natural  gas — Process  of  analysis — The  analysis  of 
mine  air — Solutions  required — The  blood  test  for  carbon  monoxide 
— Notes  on  the  process. 


CONTENTS  •    xv 

CHAPTER  XXXII 

PAGE 

THE  ANALYSIS  OP  CLAYS  AND  OTHER  SILICATES 296 

Determination  of  the  alkalis  by  J.  Lawrence  Smith  method — 
Notes  on  silicate  analysis — Analysis  of  blast-furnace  slags — Short 
method — The  determination  of  the  lime  and  the  magnesia — The 
determination  of  the  silica  and  the  alumina — Determination  of  the 
alumina  as  phosphate — Manganese — Mineral  analysis  of  clays — 
Determination  of  silica,  alumina,  lime  and  magnesia  in  iron  ores — 
Silica — Aluminum — Manganese — Lime  and  magnesia — Phenyl- 
hydrazine  Method  for  Alumina. 

CHAPTER  XXXIII 

SOFTENING  WATER  FOR  BOILER  USE      310 

Outline  process  for  the  analysis — Calculation  of  the  results. 

CHAPTER  XXXIV 
CALCULATION  OF  NORMAL  SOLUTIONS 315 

TABLES 317 

INDEX  .  .  337 


INTRODUCTION 

Before  beginning  the  course  in  special  analysis  given  in  these 
notes,  the  student  is  supposed  to  be  familiar  with  the  ordinary 
qualitative  reactions  of  the  acids  and  bases,  the  preparation  of 
reagents,  and  so  much  of  the  general  methods  of  quantitative 
analysis  as  includes  the  use  of  the  balance  and  weights,  the 
ordinary  operations  of  filtration,  washing,  drying,  igniting,  and 
weighing  of  precipitates,  the  evaporation  of  solutions,  and  also 
the  use  and  calibration  of  graduated  glassware. 

A  careful  study  of  the  first  two  sections  of  Fresenius's  "System 
of  Quantitative  Analysis,"  the  first  40  pages  of  Tread  well-Hall's 
"Analytical  Chemistry,"  Vol.  2,  and  especially  Foulk's  "Quanti- 
tative Analysis,"  Part  1,  is  advisable  in  regard  to  all  these  points 
of  manipulation. 

In  addition  to  the  above  a  few  general  precautions  and  explana- 
tions are  necessary  and  should  never  be  overlooked. 

In  adding  reagents  to  produce  any  given  effect  it  is  important 
that  the  right  amount  be  used.  To  determine  what  this  will  be 
demands  a  thorough  knowledge  of  what  is  to  take  place.  In  the 
descriptions  of  the  various  processes  these  amounts  are  approxi- 
mately indicated,  but  it  is  impossible  to  provide  in  this  way  for  all 
contingencies.  Therefore,  if  the  amount  of  reagent  directed  fails 
to  do  the  work  it  must  be  increased  or  diminished  as  may  appear 
necessary.  Thus  in  every  case  where  a  precipitate  is  formed,  it 
is  essential  that  the  filtrate  be  tested  by  a  further  addition  of  the 
reagent  to  make  sure  that  the  precipitation  is  complete.  This  is 
best  done  by  adding  the  reagent  to  a  small  portion  of  the  liquid 
in  a  test-tube,  and  if  a  precipitate  forms,  returning  this  to  the  main 
volume;  often  a  little  of  the  clear  liquid  over  the  precipitate  can 
be  tested  in  this  way  before  filtration. 

The  purity  of  the  reagents,  even  if  marked  "c.p.,"  should 
always  be  tested.  In  many  cases  it  is  necessary  to  run  a  "  blank  " 
determination  by  going  through  the  process  with  the  reagents 
alone,  leaving  out  the  substance  to  be  tested.  The  amount  of 

xvii 


xviii  INTRODUCTION 

any  impurity  which  would  affect  the  result  can  be  thus  determined 
and  allowed  for. 

A  process  should  be  tested  by  repeated  determinations  made 
on  different  amounts  of  the  substance.  Agreement  of  the  results 
in  this  case  is  a  better  indication  of  accuracy  than  if  the  same 
amounts  are  taken  in  each  determination.  Also  each  process 
must  be  tested  on  material  of  known  composition,  such  as  the 
Government  standards.  Every  laboratory  should  have  these 
standards.  This  cannot  be  too  strongly  insisted  upon. 

The  amounts  of  material  prescribed  in  the  descriptions  of  the 
processes  are  those  most  generally  used.  They  may  be  changed 
provided  the  amounts  of  the  reagents  be  varied  to  correspond. 

In  many  of  the  processes  the  calculations  may  be  greatly  sim- 
plified by  taking  "factor  weights"  of  the  material  instead  of 
even  grams.  This  consists  in  weighing  out  an  amount  of  the  sub- 
stance equal  to  the  fraction  that  the  material  to  be  determined 
forms  of  the  precipitate  weighed.  When  this  is  done  the  weight 
of  the  precipitate  in  grams  multiplied  by  100  will  give  directly 
the  percentage  sought.  If  the  factor  weight  is  inconveniently 
large  or  small  some  simple  multiple  of  it  can  be  taken  and  the 
result  estimated  accordingly. 

For  example:  one  gram  of  BaS04  contains  0.137  gram  S,  and  if 
ten  times  this  factor  (1.37  grams)  of  any  substance  is  taken  for  the 
determination  of  sulfur,  each  milligram  of  BaSO4  obtained  rep- 
resents 0.01  per  cent,  of  sulfur.  A  table  of  convenient  fac- 
tors of  this  kind  is  added  at  the  end  of  this  book  and  the  weights 
there  given  may  be  used,  when  desirable,  in  place  of  those  directed 
in  the  processes. 

A  similar  method  is  often  used  in  weighing  out  material  for 
volumetric  determinations  when  a  standard  solution  is  used  of 
which  the  value  of  1  c.c.  is  determined  experimentally  and  is  not 
an  aliquot  part  of  a  gram.  For  illustration  see  directions  for  the 
volumetric  determination  of  lime,  page  18. 

Every  chemist  should  have  a  good  microscope  in  his  laboratory 
and  use  it  frequently,  especially  when  unusual  or  strange  material 
is  sent  to  him  for  analysis.  This  will  be  a  great  help  in  showing 
him  the  nature  of  the  material  and  will  prevent  him  from  wasting 
time  on  useless  determinations  and  from  omitting  those  that 
ought  to  be  made.  The  microscope  should  have  the  proper 


INTRODUCTION  xix 

attachment  for  studying  material  under  polarized  light.  For 
metal  examination  the  microscope  should  have  provision  for 
illuminating  the  object  with  vertical  illumination. 

The  methods  of  analysis  given  in  this  book  are  of  as  universal 
application  as  possible.  When  a  large  number  of  determinations 
of  a  certain  kind  are  made  in  a  laboratory,  the  details  of  manipu- 
lation can  be  arranged  so  as  to  save  much  time  and  expense. 
For  an  exhaustive  discussion  of  this  subject  see  Ridsdale, "  Mechan- 
icalizing  Analysis  as  an  Aid  to  Accuracy  and  Speed  for  Com- 
mercial Purposes,"  J.  Iron  and  Steel  Inst.,  1911,  No.  1,  pp.  332- 
375,  and  Proc.  Cleveland  Inst.  of  Eng.,  1911-1912,  No.  4,  p.  149. 
The  acids  and  ammonium  hydroxide  solution  used  in  this  book 
are,  unless  otherwise  stated,  of  the  following  specific  gravities : 
Hydrochloric  acid,  1 . 19 

Nitric  acid,  1.42 

Sulfuric  acid,  1 . 84 

Ammonium  hydroxide,  0 . 90 


METALLURGICAL  ANALYSIS 

CHAPTER  I 

THE  SELECTION  AND  PREPARATION  OF  SAMPLES  FOR 

ANALYSIS 

General  Principles. — The  object  sought  by  the  technical  an- 
alyst is  to  ascertain  the  average  composition  of  some  particular 
lot  of  material — for  example,  a  carload  of  ore,  an  ingot  of  metal 
or  a  bin  full  of  coal. 

The  amount  of  material  treated  in  the  laboratory  is  of  necessity 
limited  to  a  few  grams.  The  preparation  of  this  small  portion 
so  that  its  analysis  shall  correctly  represent  the  composition  of 
the  mass  from  which  it  is  taken  constitutes  the  operation  of 
"sampling." 

The  general  mode  of  procedure  is  to  take  from  the  mass  in 
question  several  portions  selected  from  different  points,  and  con- 
taining coarse  and  fine  material  in  as  nearly  as  possible  the  same 
proportion  as  they  exist  in  the  mass  as  a  whole.  This  large 
sample  which  may  weigh  from  a  fraction  of  a  pound  to  a  ton, 
according  to  the  amount  of  material  the  chemist  has  to  examine, 
as  well  as  to  the  extent  of  variation  permissible  in  the  results,  is 
then  crushed  to  %  in.  or  smaller,  thoroughly  mixed  and  sub- 
divided by  "  quartering,"  until  a  sample  of  about  10  Ib.  is  ob- 
tained. This  is  pulverized  and  all  put  through  a  6-mesh  sieve, 
well  mixed  and  again  subdivided,  till  a  sample  of  100  to  300 
grams  is  obtained,  which  is  put  through  an  80-  to  100-mesh 
sieve  and  bottled  for  use. 

The  operation  of  " quartering"  is  conducted  as  follows:  The 
material  after  being  well  mixed  by  shoveling  is  formed  into  a 
pile  which  is  then  flattened  out  by  a  spiral  motion  of  the  shovel. 
This  pile  is  then  divided  into  four  quarters  by  cutting  across  at 
right  angles. 

Two  diagonally  opposite  quarters  are  selected  and  the  inter- 

1 


2  METALLURGICAL  ANALYSIS 

mediate  ones  removed.  Care  should  be  taken  to  brush  away 
carefully  all  the  material  of  the  rejected  quarters.  The  two  re- 
maining ones  are  then  mixed  together  and  the  operation  repeated 
until  a  sufficient  reduction  in  bulk  is  made. 

However,  if  the  apparatus  is  available,  it  is  best  to  perform 
the  quartering  mechanically  by  a  riffle  sampler  or  an  apparatus 
like  the  Foster-Coolidge  automatic  sampling  machine,  especially 
if  many  large  samples  are  to  be  handled.  These  automatic 
samplers  are  more  accurate  than  the  hand  quartering  and  much 
more  rapid. 

The  errors  in  sampling  may  be  many  times  larger  than  those  of 
the  chemical  analysis,  and  it  is  necessary  for  the  chemist  to  strictly 
supervise  the  sampling  of  the  materials  which  he  is  to  analyze. 
Otherwise  the  value  of  his  work  may  be  greatly  reduced  because 
of  the  sample  being  non-representative  of  the  material  it  is  sup- 
posed to  represent. 

The  errors  in  sampling  may  be  due  to  faulty  methods  of  taking 
the  sample,  as,  for  instance,  taking  one  or  several  lumps  of  ore  or 
coal  from  a  carload  when  the  carload  is  composed  of  materials  of 
different  composition.  Further,  it  may  be  very  difficult  to  secure 
a  correct  sample  because  of  the  heterogeneous  composition  of  the 
material  and  the  irregular  distribution  of  the  different  materials 
of  the  shipment.  Thus,  coal  is  contaminated  with  slate  and 
pyrite  which  may  be  very  unevenly  distributed.  In  the  sampling 
of  metals  the  great  sources  of  error  are  due  to  segregation  of  the 
components  of  the  metal  and  contamination  of  the  sample  with 
metal  and  oil  from  the  drill. 

In  sampling  minerals,  as  coal  and  iron  ore,  it  is  necessary  for 
the  sampler  to  keep  in  mind  the  importance  of  the  "size  weight" 
ratio.  That  is,  it  is  necessary  to  maintain  the  sample  at  all  times 
so  large  that  the  loss  or  gain  of  a  lump  as  large  as  the  largest 
lump  in  the  sample  and  of  whatever  composition  would  not 
affect  the  accuracy  of  the  sample  noticeably.  Further,  it  is  neces- 
sary that  in  quartering  the  sample,  the  sample  be  kept  crushed  so 
fine  that  the  gain  or  loss  of  the  largest  lump  present,  of  whatever 
composition,  will  not  noticeably  affect  the  sample.  In  other 
words,  it  is  necessary  that  the  sampler  be  a  man  of  intelligence 
and  that  he  use  his  intelligence  in  sampling. 

Many  variations  from  the  general  procedure  will  be  necessary 


SAMPLES  FOR  ANALYSIS  3 

with  different  materials.     The  following  general  principles  may 
be  stated  as  a  guide: 

1.  As  to  the  size  of  the  original  large  sample.     This  must  be 
greater  as  the  material  is  less  homogeneous  and  as  the  importance 
of  the  exact  determination  of  any  ingredient  increases.     Thus, 
a  limestone  can  easily  be  sampled;  but  a  gold  or  silver  ore  con- 
sisting of  small,  detached  fragments  of  a  very  valuable  material 
in  a  valueless  rock  may  require  the  fine  crushing  of  the  whole 
mass  of  ore  and  its  careful  mixing  and  subdivision,  to  secure  an 
"  aver  age  assay." 

2.  Materials  of  decidedly  different  specific  gravities  require 
great   care   to   prevent   separation   into   layers   during   mixing. 
(Quartering  constitutes  a  fair  safeguard  against  this  source  of 
error.) 

3.  When  the  ore  is  sifted,  every  particle  must  go  through  the 
sieve.     The  harder  parts,  which  are  left  unbroken  till  the  last,  are 
often  of  different  composition  from  the  softer  and  first  pulverized 
portions,  and  if  rejected  would  cause  serious  error. 

4.  Certain  ores  and  slags  contain  particles  of  metal  which  can- 
not be  pulverized.      In  this  case  the  grains  of  metal  not  passing 
through  the  sieve  must  be  collected  and  weighed.     The  portion 
passing  through  the  sieve  is  also  weighed.     The  metal  and  the 
siftings  are  then  analyzed  separately,  and  the  two  analyses  com- 
bined in  the  ratio  of  the  relative  weights. 

Sampling  of  Metals. — The  sampling  of  metals  presents  many 
difficulties.  Melted  metals  can  be  sampled  during  pouring  by 
taking  a  little  at  the  beginning,  middle  and  end  of  the  cast,  and 
averaging  the  three  analyses. 

In  general  it  may  be  stated: 

1.  Qast  ingots  are  not  homogeneous.     Drillings  from  different 
portions  will  show  different  analyses.     Hence,  drillings  from  a 
number  of  points  must  be  well  mixed.     A  single  "pig"  of  cast- 
iron  may  vary  largely  in  composition  from  top  to  bottom. 

2.  In  tapping  a  mass  of  metal  from  a  furnace,   different  por- 
tions of  the  "run"  will  show  differences  in  composition.     Thus, 
a  "bed"  of  pig-iron  will  show  wide  variations  in  silicon  and  sulfur 
between  the  top  and  bottom  of  the  cast. 

3.  In  some  metals  the  operation  of  drilling  will  result   in  a 
separation;  for  example,  in  drilling  pig-iron,  the  fine  portion  will 


4  METALLURGICAL  ANALYSIS 

be  of  different  composition  from  the  coarse;  hence,  careful  mix- 
ing of  the  drillings  is  necessary. 

WEIGHING  OUT  FROM  THE  LABORATORY  SAMPLE 

In  this  operation  the  tendency  of  materials  of  different  specific 
gravity  to  separate  must  never  be  lost  sight  of.  The  substance 
should  be  carefully  mixed  upon  a  sheet  of  glazed  paper  and  small 
portions  taken  from  different  parts. 

A  second  source  of  error  is  the  separation  of  coarse  and  fine,  as 
in  metal  drillings.  Great  care  is  necessary  to  avoid  serious 
difficulty  here.  The  drillings  may  be  moistened  with  alcohol  to 
make  them  adherent,  and  then  small  portions  may  be  separated, 
to  be  subsequently  accurately  weighed  when  dry  (SHIMER). 

Dirty  pig-iron  samples  are  frequently  sent  to  the  chemist,  the 
drillings  being  contaminated  by  sand,  wood,  grease,  etc.  These 
may  be  cleaned  from  sand  with  a  magnet  and  from  grease  by 
washing  with  ether,  but  the  analytical  results  on  such  samples 
should  never  be  regarded  as  entirely  satisfactory. 

ESTIMATION  OF  MOISTURE 

Many  materials  (ores,  clays,  limestones,  etc.)  as  sampled  in 
bulk  are  often  too  damp  to  pulverize.  Such  samples  must  be 
dried  on  a  steam  bath  or  by  other  means,  and  the  loss  of  weight 
determined.  The  weighing  can  be  done  on  a  portion  of  the 
crushed  and  mixed  material  which,  after  drying,  is  added  to  the 
rest  of  the  air-dry  sample.  It  is  also  always  well  to  determine 
moisture  in  the  final  sample,  and  allow  for  it  if  present.  The 
temperature  for  drying  must  not  much  exceed  100°C.,  or  water 
of  composition  may  be  expelled. 

The  analysis  may  be  stated  on  the  "dry  basis/'  but  should 
also  be  calculated  on  the  basis  of  the  wet  material. 

For  example,  a  cargo  of  iron  ore  was  sampled  in  the  vessel 
while  unloading,  as  follows:  After  the  bottom  of  the  boat  was 
reached,  portions  of  the  ore  were  taken  every.  18  in.  from  the 
top  to  the  bottom  of  the  sloping  sides  of  the  ore  exposed  in  the 
hold,  including  lump  and  fine  in  the  proportions  they  formed  at 
each  point.  This  was  repeated  when  the  vessel  was  about  half 


SAMPLES  FOR  ANALYSIS  5 

unloaded.      The   total    amount   taken    was    200  Ib.      This    was 
broken  up  as  fine  as  beans,  well  mixed  by  shoveling  and  divided 
by  quartering  until  a  portion  of  10  Ib.  was  obtained,  all  being 
done  rapidly  to  avoid  loss  of  moisture. 
This  portion  was  weighed. 

Weight 9254  grams 

After  drying  in  a  pan  on  a  steam  boiler,  weight .  .    8649  grams 


Loss 605  grams 

This  was  then  pulverized  and  mixed,  and  a  portion  of  100  grams 
taken  for  the  laboratory.  This  assayed — 

Iron 58.4  per  cent. 

Then  9254  : 8649  =  58.4  : 54. 6  =  the  per  cent,  of  iron  in  the  ore 
in  its  original  condition. 

It  may  be  noted,  first,  that  many  ores  will  absorb  water  during 
the  pulverization  (the  amount  of  water  so  absorbed  will  vary 
with  the  weather) ;  second,  complete  drying  of  a  large  sample  is 
very  difficult;  third,  ordinary  corked  bottles  are  not  moisture 
proof,  and  samples  left  in  such  will  change  in  the  course  of  time, 
if  they  are  hygroscopic. 

In  the  case  of  coal,  especially  the  "dry"  or  non-coking  coals 
and  lignites,  sampling  so  as  to  preserve  the  moisture  in  the  mate- 
rial unaltered  presents  many  difficulties.  Such  coals,  when  pul- 
verized, rapidly  lose  moisture  in  dry  air  at  ordinary  temperatures, 
and  if  then  exposed  to  moist  air  partially  regain  it. 

The  original  sample  should  be  rapidly  crushed  and  quartered 
down,  avoiding  all  unnecessary  exposure  to  air.  The  final  sample 
can  be  preserved  in  rubber-sealed  "fruit  jars." 

In  preparing  the  small  fine  sample  for  analysis,  speed  and 
covered  sieves  are  necessary.  The  pulverized  material  must  be 
kept  in  bottles  with  rubber  stoppers. 

Wet  samples,  such  as  coal  from  a  "washer,"  may  be  air  dried 
at  room  temperatures  until  they  can  be  pulverized,  but  will  not 
then  show,  as  a  rule,  the  same  moisture  as  the  original  coal  before 
wetting;  hence,  if  this  coal  is  to  be  compared  with  the  coal  before 
washing,  that  should  be  similarly  air  dried. 

Where  much  work  is  done,  special  ovens  for  drying  samples 
are  of  great  assistance. 


6  METALLURGICAL  ANALYSIS 

A  wooden  or  cement  floor  is  desirable  for  quartering  large 
samples,  but  rubber  or  oil  cloth  spread  out  on  the  ground  can  be 
used. 

It  should  never  be  forgotten  that  in  grinding  hard  material 
with  metallic  apparatus  more  or  less  of  the  metal  will  go  into  the 
product.  Thus,  a  sample  of  blast-furnace  slag  ground  in  an  iron 
mortar  would  show  more  iron  than  was  actually  in  the  slag;  there- 
fore for  the  accurate  determination  of  a  small  amount  of  iron 
in  such  a  material  a  special  sample  crushed  in  agate  should  be 
prepared. 

Sampling  Coal. — In  sampling  coal  as  it  is  unloaded  from  a  car 
or  boat  small  portions  should  be  taken  at  regular  intervals  during 
unloading.  The  total  amount  will  vary  according  to  the  nature 
of  the  coal.  Of  fine  slack  about  200  Ib.  from  a  car  will  be  suffi- 
cient, while  if  the  coal  is  lump,  500  or  1000  Ib.  will  be  necessary. 
If  a  number  of  cars  are  to  be  sampled  and  the  analysis  of  the 
mixed  samples  is  to  be  made,  a  much  smaller  amount  may  be 
taken  from  each  car. 

The  entire  sample  should  be  spread  out  on  a  floor  and  the  larger 
pieces  broken  with  a  hammer,  unless  a  power  crusher  is  handy 
when  the  entire  lot  is  put  through  the  crusher.  The  crushed 
sample  is  then  well  mixed  and  quartered  by  hand  or  by  a  sampling 
machine  and  the  crushing  and  dividing  repeated  until  a  sample 
small  enough  to  send  to  the  chemical  laboratory  is  obtained.  If 
the  sample  has  been  crushed  as  small  as  %  in.  the  amount  sent 
to  the  laboratory  need  not  be  larger  than  5  Ib. 

The  laboratory  sample  when  received  is  weighed  and  thor- 
oughly air  dried  by  exposing  in  a  warm  room  for  about  36  hours 
or  by  drying  in  a  drier  heated  about  10°  above  the  room  tem- 
perature and  with  a  rapid  circulation  of  air.  The  sample  is  then 
weighed,  and  the  drying  continued  a  half  day  if  mere  air  drying  is 
done,  or  two  hours  if  the  drier  is  used.  The  sample  is  weighed 
again  and  if  a  loss  of  not  more  than  0.2  per  cent,  is  found  the 
drying  has  been  sufficient.  The  air-drying  loss  is  then  calculated 
in  per  cent. 

The  dried  sample  is  then  crushed  to  about  8  mesh  and  quar- 
tered to  a  pound.  It  is  again  crushed  to  10  mesh  and  quartered 
to  J^  Ib.,  and  this  is  then  ground  on  a  bucking  board  or  better  in  a 
ball  mill  until  it  will  go  through  a  60-mesh  sieve.  A  2-oz.  sample 


SAMPLES  FOR  ANALYSIS  7 

is  then  put  in  a  rubber-stoppered  sample  bottle  and  it  is  ready 
for  analysis. 

The  entire  sampling,  both  before  and  after  air  drying,  must  be 
done  as  quickly  as  possible  to  prevent  loss  or  gain  of  moisture 
during  the  sampling.  The  sample  should  not  be  ground  finer 
than  60  mesh  as  it  then  takes  up  oxygen  rapidly.  A  coarse 
sample  which  has  been  well  air  dried  may  lose  as  much  as  a  per 
cent,  of  moisture  on  being  exposed  to  the  air  a  few  minutes  after 
fine  grinding.  The  fine  sample  must  be  analyzed  promptly  even 
if  well  stoppered,  as  it  alters  rapidly  by  oxidation  and  moisture 
changes. 

If  the  large  sample  of  several  hundred  pounds  first  taken  is  wet 
or  damp  it  should  be  weighed  and  spread  out  on  a  floor  until  dry 
and  weighed  again  before  any  quartering  is  done. 

Sampling  Iron  Ores. — The  principles  are  the  same  as  for  coal. 
It  is  always  best  to  sample  the  lot  as  it  is  being  loaded  or  unloaded 
since  the  material  on  top  may  be  of  different  composition  from 
that  underneath.  At  stated  intervals  of  time  a  shovelful  is  taken. 
Or  after  the  ore  has  been  partially  removed  from  the  boat  or  car, 
leaving  cone-shaped  depressions,  the  samples  are  taken  from  the 
faces  of  these  depressions.  Thus  after  a  grab  has  removed  as 
much  ore  as  possible  from  a  hatch,  the  sampler  goes  to  the  face  of 
the  cone  and,  starting  from  the  bottom,  he  takes  trowel  samples 
at  stated  intervals  in  a  straight  line  up  one  side  of  the  cone. 
This  he  repeats  in  four  different  directions,  starting  each  time 
from  the  bottom  of  the  cone.  The  entire  sample  from  a  boat 
may  weigh  a  thousand  pounds. 

In  sampling  cars  sometimes  a  rope  net  is  spread  over  the  car 
and  a  sample  of  several  ounces  is  taken  from  underneath  each 
knot  of  the  net,  of  which  knots  the  net  will  have  about  36.  The 
same  thing  can  be  done  without  the  net.  The  ore  should  not  be 
taken  from  the  surface  but  far  enough  underneath  to  get  beyond 
the  reach  of  surface  wetting  or  evaporation.  But  it  is  always 
best  to  get  the  sample  from  the  car  while  unloading  so  as  to  get 
samples  all  through  the  mass  of  ore. 

The  sample  is  weighed  if  wet,  and  dried,  if  not  too  large,  on  a 
steam  pan  or  in  a  drying  oven  at  100°  and  weighed  again.  This 
gives  the  drying  loss.  It  is  then  crushed  to  J^-in.  size  or  smaller 
and  divided,  crushed  smaller  and  again  divided,  until  the  sample 


8  METALLURGICAL  ANALYSIS 

weighs  about  5  Ib.  and  is  about  J^-in.  mesh  size.  This  is  dried 
at  100°C.  to  constant  weight,  and  the  loss  in  weight  calculated 
in  per  cent.  The  sample  is  quartered  to  about  a  pound  and  then 
ground  to  100  mesh  in  a  disc  pulverizer  having  manganese  steel 
discs,  or  in  a  ball  mill,  or  on  a  manganese  steel  bucking-board. 
The  sample  is  then  mixed  well  and  quartered  in  a  small  riffle 
sampler  to  about  100  grams  and  bottled  in  a  rubber-stoppered 
bottle. 

If  the  original  sample  is  wet  and  too  hard  to  be  dried  conven- 
iently, a  hundred  pounds  are  accurately  weighed  and  dried  at 
100°C.  for  18  hours  and  weighed  again,  and  the  dry  ore  added  to 
the  rest  of  the  sample  which  is  then  treated  as  above  directed. 
If  100  Ib.  is  too  large  for  the  drier,  25  Ib.  may  be  taken. 

REFERENCES  ON  IRON  ORE  SAMPLING: 

WILEY,  "  Methods  used  at  Illinois  Steel  Co.,"  J.  Ind.  Eng.  Chem.,  Ill, 

103. 
CAMP,  "Methods  of  U.  S.  Steel  Corporation,"  J.  Ind.  Eng.  Chem.,  I, 

107. 

J.  Anal.  App.  Chem.,  V,  299. 
GLENN,  Trans.  Am.  Inst.  Mining  Eng.,  XX,  155. 
LANDIS,  Trans.  Am.  Inst.  Min.  Eng.,  XX,  611. 
KIDDIE,  "  Causes  of  Errors,"  Eng.  Mining  J.,  LXXXVIII,  824. 

REFERENCES  ON  COAL  SAMPLING: 
SOMERMEIER,  "Coal,"  pp.  57-79. 
BAILEY,  J.  Ind.  Eng.  Chem.,  I,  161. 

Sampling  of  Pig-iron. — When  the  iron  is  run  out  of  the  furnace 
a  spoonful  is  taken  several  times  during  the  cast,  at  least  once  at 
the  beginning,  once  at  the  middle  of  the  cast  and  once  near  the 
end.  If  the  iron  is  run  into  ladles  it  is  well  to  take  a  spoonful  from 
the  middle  of  each  ladleful.  The  spoonfuls  of  metal  are  poured 
into  cast-iron  molds  about  10X4X3  in.  outside  dimensions  and 
with  inside  dimensions  of  about  6X1%X1}4  m-  deep,  with  a 
projection  in  the  center  so  that  the  ingot  will  have  a  notch  in 
order  that  it  may  be  easily  broken  to  observe  the  fracture.  The 
ingot  should  be  drilled  deeply  in  at  least  two  places  to  get  drillings 
for  analysis.  The  drillings  from  all  the  ingot  samples  from  a  cast 
are  mixed  for  analysis. 

The  drill  must  be  worked  dry  (without  oil)  and  care  should  be 
taken  to  reject  the  outer  "skin"  of  the  ingot  or  bar,  which  is 
usually  contaminated  with  matter  not  properly  belonging  in  the 


SAMPLES  FOR  ANALYSIS  9 

analysis.  Cast-iron  is  frequently  sampled  by  pouring  a  little  of 
the  molten  metal  into  water.  This  makes  the  iron  white  and 
very  brittle.  These  so-called  "shot  samples"  and  similar  brittle 
material  as  "spiegel  iron"  and  "wash  metal,"  which  are  too  hard 
to  drill,  must  be  broken  into  small  fragments  with  a  sledge  ham- 
mer and  several  pieces  pulverized  in  a  steel  mortar.  A  very 
efficient  mortar  for  this  purpose  can  be  made  by  boring  a  hole 
2  in.  deep  and  1  in.  in  diameter  into  a  block  of  tool  steel  about  3 
in.  square  and  4  in.  high.  Fit  this  with  a  steel  "rammer"  cut 
from  a  round  bar  and  about  3  in.  longer  than  the  hole.  It  must 
be  only  slightly  smaller  than  the  hole  in  the  block.  Both  block 
and  rammer  must  be  well  hardened.  By  dropping  a  fragment  of 
metal  into  the  hole,  inserting  the  rammer  and  pounding  it  vigor- 
ously with  a  heavy  hammer  the  hardest  material  is  soon  reduced 
to  a  fine  sand. 

In  sampling  all  metal  ingots  and  billets  it  must  be  remembered 
that  the  metal  will  vary  in  composition  from  place  to  place  be- 
cause of  segregation,  and  so  must  be  drilled  in  several  places  and 
if  possible  clear  through. 

REFERENCES  ON  SAMPLING  METALS: 

"Methods  used  by  the  U.  S.  Steel  Corporation,"  J.  Ind.  Eng.  Chem., 

IV,  801. 

SHIMER,  Trans,  lust.  Mining  Eng.,  XIV,  760. 
KELLER,  "Copper  Bar  Sampling,"  Eng.  Mining  J.,  XCIII,  703. 

Sampling  Equipment. — The  following  or  similar  equipment  is 
necessary  in  any  laboratory  which  does  a  large  amount  of  work: 

1.  A  drill  press,  preferably  a  power  drill  press. 

2.  A  swing  hammer  pulverizer  equipped   with  a  chute  for 
mechanically  dividing  the  samples.     The  Jeffrey  "baby  pulver- 
izer," made  by  the  Jeffrey  Manufacturing  Company  of  Colum- 
bus, Ohio,  has  a  capacity  of  1000  Ib.  of  coal  per  hour  reduced  to 
y±  in.     It  uses  about  7  h.p. 

3.  A  hand  or  power  jaw  crusher  is  especially  useful  for  crushing 
hard  rock,  but  is  also  satisfactory  for  coal  crushing  to  about  J£ 
in.     The  "Chipmunk"  crusher,  made  by  the  Braun  Corporation 
of  Los  Angeles,  will  crush  200  Ib.  per  hour  to  l£-m.  size  in  the 
small  crusher  and  1000  Ib.  per  hour  in  the  large  size.     About  2  h.p. 
is  required. 

4.  A  pair  of  6-in.  rolls  is  needed  to  crush  from  Y±-\i\.  size  to 


10 


METALLURGICAL  ANALYSIS 


10  mesh.  The  6-in.  rolls  made  by  the  American  Concentrator 
Company  of  Joplin,  Mo.,  can  reduce  fifty  to  one  hundred  4-lb. 
samples  from  Y±  in.  to  10  mesh  in  a  day. 

5.  For  reducing  the  10-mesh  coal  samples  to  60  mesh  or  finer  a 
pebble  ball  mill  is  very  efficient,  especially  as  it  prevents  moisture 
changes  during  the  grinding.  A  four-jar  mill  such  as  the  one 
made  by  The  Abbe  Engineering  Company  of  New  York  will 
grind  40  to  50  samples  per  day  if  extra  jars  are  provided. 


FIG.   1. 


6.  For  occasional  sampling  a  bucking  board  with  heavy  muller 
answers  the  purpose  of  fine  grinding  any  mineral  sample.     It  is 
best  made  of  manganese  steel  or  chrome  steel.     These  steels  are 
so  hard  that  they  wear  very  slowly. 

7.  A  mechanical  divider  such  as  the  Foster-Coolidge  machine 
is  almost  a  necessity  when  large  numbers  of  large  samples  are 
handled.     For  samples  weighing  less  than  100  Ib.  the  riffle  sam- 
pler shown  in  Fig.  1  answers  all  purposes  unless  a  large  number 
of  samples  are  handled. 

8.  Coarse  wooden  frame  sieves  from  1  in.  to    ±  in.  and  brass 


SAMPLES  FOR  ANALYSIS 


11 


sieves  from  10  mesh  to  120  mesh  are  necessary  in  the  sampling 
room. 

9.  For  fine  grinding  of  ores  an  Her  or  other  disc  pulverizer  is 
indispensable  if  many  samples  are  to  be  ground. 


FIG.  2. 

10.  For  drying  coarse  ores  and  especially  coals  the  oven  shown 
in  Fig.  2  is  convenient.     A  steam-heated  pan  or  table  is  also  use- 
ful, especially  for  wet  ores. 

11.  A  large  platform  scale  for  weighing  up  to  1000  Ib.  and  a 
Troemner  solution  scale  No.    80  for  weighing  up  to  5  Ib.  are 
necessary. 


CHAPTER  II 
THE  ANALYSIS  OF  LIMESTONES 

The  constituents  to  be  determined  are  silica,  oxide  of  iron,  oxide  of 
aluminium,  carbonate  of  calcium,  and  carbonate  of  magnesium.  The 
silica  is  present  chiefly  as  quartz,  clay,  and  other  silicates.  Beside 
oxide,  iron  may  be  present  as  ferrous  carbonate,  or  combined  with  sul- 
fur as  pyrite.  Small  amounts  of  phosphoric  acid  and  sulfates  are 
also  often  present,  and  are  determined  as  in  iron  ores.  Since  the  water 
combined  in  the  clay  and  other  constituents  such  as  organic  matter  are 
not  determined,  the  results  will  usually  not  total  up  to  100  per  cent. 

In  examining  limestone  quarries  to  determine  the  quality  of  the  stone 
for  furnace  flux,  lime  or  cement  manufacture,  the  rock  should  be  sampled 
layer  by  layer,  as  different  layers  usually  vary  greatly  from  each  other 
in  composition,  while  material  from  the  same  layer  (or  "bed")  is  likely 
to  be  of  uniform  composition.  The  stone  generally  ranks  in  quality 
according  to  the  carbonate  of  lime. 

Process  of  Analysis. — Weigh  1  gram  of  the  finely  ground  sample 
and  transfer  it  to  a  platinum  crucible.  Add  %  gram  of  sodium 
carbonate,  and  mix  well  with  the  sample  in  the  crucible.  Then 
heat  cautiously — to  prevent  spattering  due  to  too  rapidly  liber- 
ated carbon  dioxide — and  finally  heat  over  a  blast  or  large  Meker 
burner  for  10  minutes.  Transfer  the  sintered  mass  to  a  casserole, 
and  moisten  with  water.  Clean  out  the  crucible  with  30  c.c.  of 
1:1  HC1,  and  pour  into  the  casserole.  Heat  until  the  cake  is 
dissolved,  using  a  heavy  stirring  rod  to  break  it  up  if  necessary. 
It  should  go  completely  into  solution.  Then  evaporate  to  dry- 
ness,  and  heat  to  120°C.  for  one-half  hour  to  render  the  silica  in- 
soluble. Cool  the  casserole  and  drench  the  contents  with  20  c.c. 
of  1  : 1  HC1,  and  heat  until  everything  has  gone  into  solution 
except  the  silicic  acid.  Filter  on  an  ashless  filter,  and  wash 
well  (about  eight  times)  with  hot  dilute  HC1,  then  several  times 
with  water.  The  filtrate  will  contain  perhaps  1  per  cent,  of  the 
total  silica.  For  exact  work,  evaporate  the  filtrate  to  dryness, 
dissolve  the  residue,  filter  and  wash  as  above.  Burn  the  two 

12 


THE  ANALYSIS  OF  LIMESTONES  13 

filter  papers  and  their  contents  together  in  a  platinum  crucible, 
and  ignite  the  silica  over  a  blast  for  15  minutes.  Weigh  the  cru- 
cible and  contents,  add  a  drop  of  sulfuric  acid  and  5  c.c.  of  HF, 
and  evaporate  to  dryness  to  expel  the  SiF4.  Ignite  and  weigh 
again.  The  loss  in  weight  is  SiC>2.  When  great  accuracy  is  not 
required,  and  the  silica  is  small  in  amount,  one  dehydration  may 
be  sufficient  and  the  use  of  H-F  may  be  dispensed  with. 

After  driving  off  the  SiF4  a  small  residue  of  oxides  of  iron, 
aluminium,  titanium  and  phosphorus  may  be  left  in  the  crucible. 
Transfer  this  residue  to  the  filtrate  from  the  silica  by  moistening 
with  HC1,  and  rubbing  with  a  policeman  to  loosen  it,  and  then 
washing  out  of  the  crucible  by  means  of  a  jet  of  water  from  the 
wash  bottle. 

To  the  filtrate,  the  volume  of  which  should  be  about  100  c.c., 
carefully  add  NH4OH  until  it  just  smells  distinctly  of  NH3. 
Should  the  precipitate  be  light  colored  and  large  in  amount,  in- 
dicating the  probable  precipitation  of  Mg(OH)2,  add  5  c.c.  HC1 
and  again  NH4OH  as  before.  Now  boil  the  liquid  about  three 
minutes  or  until  the  odor  of  NH3  is  nearly  gone.  Remove  from 
the  heat,  allow  the  precipitate  to  settle,  filter  on  an  ashless  filter 
and  wash  well  with  a  hot  1  per  cent,  solution  of  NH4NOa. 
Ignite  and  weigh  the  precipitate  of  Fe2O3,  A^Oa,  P20s,  Ti(>2.  If 
the  precipitate  of  iron  and  aluminium  hydroxides  is  large,  it 
should  be  washed  from  the  filter  paper  back  into  the  beaker,  dis- 
solved in  HC1,  precipitated  with  ammonia,  filtered  and  washed 
again.  For  strictly  accurate  results,  two  precipitations  should 
always  be  made.  The  iron  and  titanium  may  be  determined  in 
the  ignited  precipitate  after  fusion  with  KHSO4.  For  details 
see  the  Analysis  of  Clays,  page  298.  The  P2O5  is  best  determined 
in  another  sample,  if  desired.  The  sum  of  the  oxides  of  iron, 
titanium,  silicon  and  phosphorus  when  deducted  from  the  total 
weight  of  the  oxides  gives  the  weight  of  the  alumina. 

Dilute  the  filtrate  from  the  iron,  aluminium  hydroxide,  etc., 
to  about  200  c.c.  If  it  is  not  distinctly  alkaline  add  5  to  10 
drops  of  NH4OH,  heat  to  boiling  and  slowly  add  80  c.c.  of  a 
solution  of  (NH4)2C2O4  also  heated  to  boiling.  Use  a  saturated 
solution  of  the  salt  diluted  with  an  equal  volume  of  water.  Stir 
well  during  the  addition  of  the  reagent  and  for  a  minute  or  two 
afterward,  then  set  aside  until  the  precipitate  of  CaC204  has 


14  METALLURGICAL  ANALYSIS 

settled  completely.  Decant  the  liquid  through  a  9-cm.  filter 
without  disturbing  the  precipitate,  wash  the  precipitate  once  by 
decantation,  using  about  50  c.c.  of  boiling  hot  water,  then  dissolve 
the  precipitate  in  5  c.c.  HC1,  add  100  c.c.  water,  heat  to  boiling, 
add  NH4OH  until  just  alkaline,  then  5  c.c.  more  of  (NH4)2C2O4 
solution.  Let  settle,  filter,  transfer  the  precipitate  to  the  filter 
paper  and  wash  six  or  seven  times  with  hot  water.  When  the 
filtrate  is  to  be  concentrated  for  the  determination  of  the  mag- 
nesia, set  aside  the  first  filtrate  and  decanted  liquid,  and  catch 
the  subsequent  washings  in  a  separate  beaker.  Concentrate 
these  by  boiling  down  to  a  small  volume  and  then  add  them  to 
the  first  portion. 

Dry  the  precipitate  thoroughly,  detach  it  as  far  as  possible 
from  the  filter,  put  it  in  a  weighed  No.  0  porcelain  crucible,  burn 
the  filter  carefully  on  a  platinum  wire  and  add  the  ash  to  the 
contents  of  the  crucible.  Now  drop  concentrated  H2SC>4  on  to 
the  precipitate  until  it  is  well  moistened,  but  avoid  much  excess. 
Heat  the  crucible  (working  under  a  "hood"  'to  carry  off  the 
fumes),  holding  the  burner  in  the  hand  and  applying  the  flame 
cautiously  until  the  swelling  of  the  mass  subsides,  and  the  excess 
of  H2SO4  has  been  driven  off  as  white  fumes.  Finally  heat  to  a 
cherry  red  for  five  minutes.  Do  not  use  the  blast  lamp.  Cool 
and  weigh  the  CaSO4.  The  weight  of  the  CaSO4  multiplied  by 
0.7350  gives  the  amount  of  CaCO3  in  the  sample,  or  if  multiplied 
by  0.4119  gives  the  amount  of  CaO. 

Instead  of  changing  the  oxalate  to  sulfate  it  is  better  to  place 
the  precipitate  and  filter  paper  in  a  platinum  crucible,  burn  off 
the  paper,  cover  the  crucible  with  a  lid  and  ignite  at  the  high 
temperature  of  the  blast  lamp  or  a  good  Meeker  burner  for  15 
minutes,  cool  in  a  desiccator  and  weigh  as  CaO.  This  multiplied 
by  1.7847  gives  the  weight  of  the  CaCO3.  The  CaO  should  not 
stay  in  the  desiccator  more  than  an  hour  before  weighing.  The 
blast  flame  should  be  inclined,  not  vertical. 

The  filtrate  from  the  CaC2O4  should  be  concentrated  to  300  c.c. 
if  over  that  volume;  should  any  MgC2O4  separate,  dissolve  it 
by  adding  a  little  HC1.  Add  5  c.c.  of  NH4OH,  heat  to  boiling 
and  add  10  c.c.  or  a  sufficient  quantity  of  a  saturated  solution  of 
Na2HP04.  Add  a  few  cubic  centimeters  more  of  NH4OH,  then 
allow  to  cool  with  occasional  vigorous  stirring.  The  precipitate 


THE  ANALYSIS  OF  LIMESTONES  15 

of  MgNH4PO4  should  be  allowed  to  settle  until  the  liquid  is 
perfectly  clear  (about  two  hours).  Filter  and  wash  with  water 
containing  one-tenth  its  volume  of  NH4OH,  sp.  gr.  0.90,  and  a 
little  NH4NO3.  Ten  cubic  centimeters  of  the  phosphate  solution 
is  sufficient  for  about  20  per  cent.  MgCO3;  for  dolomites  more 
must  be  added.  When  there  is  a  large  amount  of  MgO  present, 
the  precipitate  should  be  dissolved  in  a  little  HC1,  made  alkaline 
with  NH4OH  and  precipitated  as  before,  using  only  1  or  2  c.c.  of 
phosphate  solution.  Dry  the  precipitate,  detach  it  from  the  filter 
paper,  and  burn  the  paper  on  a  platinum  wire;  now  ignite  the  pre- 
cipitate and  filter  ash  in  a  porcelain  crucible,  first  heating  carefully 
over  a  Bunsen  burner  till  all  volatile  matter  is  driven  off  and  it 
has  been  at  a  dull  red-heat  for  some  minutes,  then  finishing  over 
the  blast  lamp  for  five  or  ten  minutes.  The  ignited  precipitate 
is  Mg2P2O7,  the  weight  of  which  multiplied  by  0.7572  gives 
the  MgCO3,  or  by  0.3621  gives  the  MgO  in  the  sample. 

Notes  on  the  Process. — 1.  Limestones  generally  contain  silicates. 
When  the  sample  is  heated  to  a  high  temperature,  silicates  of  lime  and 
sodium,  if  sodium  carbonate  has  been  used,  are  formed,  which  are  solu- 
ble in  HC1  with  the  formation  of  silicic  acid.  This  is  made  insoluble 
by  evaporation  to  dryness,  changing  the  silicic  acid  into  SiO2  more  or 
less  hydrated.  The  presence  of  CaCl2  renders  the  dehydration  of  the 
silicic  acid  easy  at  the  temperature  of  the  water  bath.  A  much  higher 
temperature  is  to  be  avoided  as  silica  may  re  combine  with  the  bases, 
especially  MgO,  and  so  either  be  redissolved  on  treatment  with  acid  or 
render  bases  insoluble.  One  evaporation  leaves  perhaps  1  per  cent,  of 
the  silica  soluble,  and  even  after  two  evaporations  some  silica  will  be 
found  with  the  iron  and  alumina  precipitate.  The  silica  must  be  filtered 
off  after  each  evaporation. 

2.  The  silica  retains  alkaline  salts  tenaciously.     It  must  be  washed 
thoroughly,  first  with  hot  water  acidulated  with  HC1,  then  with  cold 
water  until  the  filtrate  gives  no  test  for  chlorine  when  tested  with  AgNO3. 

3.  The  Si02  must  be  ignited  to  constant  weight,  as  it  retains  water 
most  tenaciously.     A  blast  lamp  is  necessary  to  remove  the  last  traces. 

4.*  Fe(OH)3  and  A1(OH)3  are  insoluble  in  solutions  of  NH4C1,  but  a 
large  excess  of  NH4OH  holds  A1(OH)3  in  solution  to  a  slight  extent. 
This  is  separated  by  boiling  off  the  excess  of  NH4OH  or  by  the  presence 
of  a  large  excess  of  NH4C1.  Too  much  boiling  renders  the  iron  and  alu- 
mina precipitates  slimy  and  difficult  to  wash  and  filter.  Hence  care  is 
necessary  in  adding  the  NH4OH  to  avoid  large  excess,  so  that  a  few  min- 
utes boiling  will  be  sufficient.  The  precipitate  should  not  be  washed 


16  METALLURGICAL  ANALYSIS 

with  pure  water,  as  it  causes  some  alumina  to  go  through  the  paper. 
The  wash  solution  should  be  made  by  adding  20  c.c.  of  HN03,  sp.  gr. 
1.42,  to  a  liter  of  water  and  then  adding  NH4OH  until  alkaline. 

5.  Mg(OH)2  is  not  completely  soluble  in  NH4OH  unless  sufficient 
NH4C1  be  present  to  decrease  the  ionization  of  the  NH4OH.     It  sepa- 
rates as  a  white  precipitate  easily  mistaken  for  alumina,  so  if  the  iron 
and  aluminium  hydroxide  precipitate  is  large,  it  is  best  to  redissolve 
it  in  considerable  HC1  and  reprecipitate  with  NH4OH.     If  much  iron 
and  alumina  are  present,  the  precipitate  will  certainly  contain  CaO 
and  MgO  which  must  be  removed  by  re-solution  and  reprecipitation  as 
above  described.     Solutions  containing  NH4OH  and  CaO  will  absorb 
CO2  on  standing,  precipitating  CaC03;  hence  the  iron  and  alumina 
hydroxides  must  be  filtered  and  washed  promptly.     Distilled  water 
often  contains  C02  which  will  cause  a  precipitation  in  the  same  way; 
hence  boiling  the  water  before  use  is  best.     Cold  water  in  a  wash  bottle 
rapidly  absorbs  C02  from  the  breath;  such  water  should  never  be 
used  in  diluting  the  alkaline  liquid  holding  the  Fe(OH)3  and  A1(OH)3 
precipitate. 

6.  Calcium  oxalate  is  very  insoluble,  but  it  is  a  difficult  precipitate  to 
filter  and  wash  if  not  formed  exactly  right.     On  gentle  ignition  below 
visible  redness  it  is  changed  to  carbonate,  and  at  still  higher  tempera- 
tures to  CaO.     The  complete  conversion  to  oxide  requires  a  rather  high 
temperature  for  considerable  time.     However,  the  change  is  easily  made 
complete  and  this  method  of  determining  the  lime  is  quite  accurate  if 
care  is  taken  to  ignite  to  constant  weight.     The  CaO  formed  is  somewhat 
hygroscopic  and  should  be  weighed  as  soon  as  cooled  in  a  desiccator. 
The  action  of  concentrated  H2S04  on  calcium  oxalate  converts  it  to 
CaS04.     The  action  is  not  violent  and  the  excess  of  H2SO4,  provided  it 
is  moderate,  can  be  driven  off  without  danger  of  loss  by  spurting.     Lumps 
in  the  crucible  should  be  broken  up  before  H2S04  is  added  and  care 
should  be  taken  that  the  entire  mass  is  moistened  by  the  H2SO4.     CaSO4 
will  stand  the  cherry  red  heat  of  a  Bunsen  burner  without  alteration, 
but  the  higher  heat  of  a  blast  lamp  will  cause  it  to  lose  S03. 

It  must  not  be  forgotten  that  any  strontium  in  the  sample  will  pre- 
cipitate with  the  calcium  as  strontium  oxalate. 

7.  Calcium   oxalate  is  somewhat  soluble  in   hot  water,  hence   care 
should  be  taken  not  to  use  unnecessarily  large  amounts  of  hot  water 
in  washing  it. 

8.  Magnesium  will  precipitate  as  oxalate  in  concentrated  solutions, 
hence  when  much  is  present  the  calcium  oxalate  should  be  dissolved  and 
reprecipitated  as  described  above.     In  the  case  of  ordinary  limestone, 
this  is  not  necessary  if  the  calcium  is  precipitated  in  properly  diluted 
solutions,  unless  very  accurate  results  are  desired. 


THE  ANALYSIS  OF  LIMESTONES  17 

9.  On  concentrating  the  filtrate  from  the  calcium  oxalate,  a  crystal- 
line precipitate  of  magnesium  oxalate  will  sometimes  separate.  This 
can  be  redissolved  in  HC1  and  added  to  the  solution.  If  it  contains  any 
calcium  oxalate  it  will  leave  a  milky  solution  clearing  slowly. 

10-  As  the  liquid  in  which  the  magnesium  is  precipitated  contains  all 
the  material  added  in  the  analysis,  careless  addition  of  reagents  may  give 
so  strong  a  solution  of  ammonium  and  sodium  salts  that  the  precipita- 
tion of  the  magnesium  phosphate  will  not  take  place  promptly.  How- 
ever, the  precipitation  will  be  complete  in  time.  To  get  rid  of  the  ammo- 
nium salts,  the  filtrate  should  be  evaporated  to  dryness  with  3  c.c.  of 
HNO3,  sp.  gr.  1.42,  for  each  gram  of  NH4C1,  which  will  decompose  and 
remove  ammonium  salts.  Then  any  remaining  magnesium  may  be 
precipitated. 

11.  There  must  be  enough  (NH4)2C204  solution  added  to  convert 
all  the  magnesium  as  well  as  the  calcium  to  oxalate  or  calcium  oxalate 
will  not  completely  precipitate. 

12.  Sodium  oxalate  being  very  sparingly  soluble  will  sometimes  sepa- 
rate with  the  magnesium  precipitate,  especially  when  the  solution  is  con- 
centrated and  much  Na2HP04  has  been  added;  in  this  case,  after  partial 
washing,  the  precipitate  must  be  dissolved  in  HC1  and  reprecipitated  by 
NH4OH. 

13.  Any  manganese  which  was  in  the  sample  will  precipitate  chiefly 
with  the  magnesium.     It  can   be  determined  very  accurately  in  the 
ignited  precipitate  colorimetrically  and  the  magnesium  results  corrected. 
Any  barium  in  the  sample  will  be  found  chiefly  in  the  filtrate  from  the 
magnesium,  but  some  will  be  with  the  calcium  and  some  perhaps  with 
the  magnesium. 

REFERENCES: 

"Silica  Separation,"  J.  Anal,  and  App.  Chem.,  Vol.  .IV,  p.  159. 

"Magnesium  Calcium  Separation,  Fresenius,  Quantitative  Analysis," 
Pars.  73,  74,  101,  104,  154. 

For  refined  methods  of  limestone  analysis  see  United  States  Geolog- 
ical Survey  Bulletin  422,  "The  Analysis  of  Silicate  and  Carbonate 
Rocks,"  by  W.  F.  HILLEBRAND. 

Instead  of  determining  the  total  silica  as  is  given  in  the  above  process, 
it  is  the  custom  in  many  places  to  determine  what  is  called  the  "in- 
soluble silicious  matter."  This  is  done  by  dissolving  the  sample  in 
strong  HC1,  evaporating  to  dryness  to  dehydrate  any  soluble  silica,  and 
then  filtering  off,  washing  and  weighing  the  residue.  Iron  and  alumina, 
lime  and  magnesia  are  then  determined  in  the  filtrate  as  in  the  filtrate 
from  the  silica.  The  insoluble  silicious  matter,  however,  generally  is 
not  all  silica.  Since  it  is  just  about  as  quick  to  ignite  and  determine 
2 


18  METALLURGICAL  ANALYSIS 

silica  accurately,   the  determination  of  "insoluble  silicious  matter" 
seems  hardly  worth  while. 

The  determination  of  C02  is  generally  not  necessary  for  technical 
purposes,  but  it  may  very  easily  be  done  by  use  of  the  apparatus  shown 
on  page  104.  A  1-gram  sample  is  placed  in  the  flask,  covered  with  water, 
and  HC1  added  slowly  so  that  not  more  than  three  or  four  bubbles  per 
second  pass  through  the  KOH  bulb.  When  effervescence  ceases,  the 
acid  in  the  flask  is  heated  to  boiling,  and  then  a  liter  of  air  is  drawn 
through  the  apparatus.  The  increase  in  weight  in  the  KOH  bulb  gives 
the  amount  of  C02.  The  KOH  bulbs  must  of  course  show  no  increase 
or  decrease  in  weight  when  a  liter  of  air  is  aspirated  through  as  a  blank 
before  the  regular  determination. 

THE  VOLUMETRIC  DETERMINATION  OF  LIME 

Instead  of  weighing  the  calcium  as  CaS04  or  CaO,  it  may  be  deter- 
mined by  measuring  the  volume  of  a  standard  solution  of  KMn04 
required  to  oxidize  the  oxalic  acid  which  it  contains.  The  precipitate 
is  first  dissolved  in  dilute  sulfuric  acid,  the  liberated  oxalic  acid  is  then 
titrated  by  KMn04.  The  reactions  may  be  summed  up  as  follows: 

5CaC204+8H2S04+2KMn04  =  5CaSO4+K2S04+2MnSO4- 
+  10C02  +  8H2O. 

This  reaction  takes  place  rapidly  at  70°C.  The  first  few  drops  of 
permanganate  color  the  liquid  and  a  few  seconds  will  elapse  before  color 
disappears,  then  the  reagent  may  be  added  rapidly.  This  delay  in 
starting  is  entirely  removed  if  a  few  drops  of  a  strong  solution  of  MnS04 
are  added  to  the  liquid  before  titration.  As  the  titration  proceeds,  rapid 
effervescence  of  C02  takes  place,  resulting  in  a  spraying  out  of  some  of 
the  liquid  unless  the  titration  is  done  in  a  flask. 

Solution  Required. — The  solution  required  is  a  standard  solu- 
tion of  potassium  permanganate.  The  same  solution  can  be 
used  as  for  the  determination  of  iron  in  ores.  The  iron  value 
multiplied  by  0.8960  gives  the  CaCO3  equal  to  1  c.c.  of  perman- 
ganate in  the  above  reaction;  however,  it  is  best  to  standardize 
the  permanganate  against  pure  Iceland  spar  or  pure  lime,  which 
is  dissolved  in  HC1,  and  the  calcium  precipitated  as  oxalate  as 
in  the  above  process. 

Process. — A.  For  limestone  low  in  magnesia. 

Weigh  out  89.6  times  the  iron  value  of  the  permanganate,  if  it 
is  desired  to  report  as  carbonate,  or  50.2  if  it  is  desired  to  report 
as  CaO.  The  sample  should  be  finely  ground.  Transfer  to  a 


THE  ANALYSIS  OF  LIMESTONES  19 

small  platinum  crucible,  and  ignite  cautiously  to  destroy  organic 
matter.  Transfer  the  ignited  powder  to  a  400  c.c.  beaker,  add  20 
c.c.  of  water,  cover  and  then  add  15  c.c.  HC1,  sp.  gr.  1.19,  and 
3  or  4  drops  of  HN03.  Boil  until  all  the  soluble  matter  is  dis- 
solved and  all  the  C02  expelled.  Wash  off  and  remove  the  cover 
and  dilute  the  liquid  to  about  150  c.c.  with  water  free  fromCO2. 
Add  NH4OH  in  slight  excess,  and  heat  to  boiling.  Then  without 
filtering  off  the  precipitated  iron  and  aluminium  hydroxides, 
precipitate  the  CaC2O4  exactly  as  in  the  gravimetric  analysis. 
Continue  the  stirring  two  or  three  minutes  after  the  addition  of 
the  hot  ammonium  oxalate  solution  and  then  let  settle  until 
nearly  clear,  which  should  require  not  over  five  minutes  if  the 
work  is  correctly  done. 

Decant  through  a  9  cm.  filter,  pouring  off  very  closely.  The 
precipitate  should  be  so  dense  as  to  render  this  easy.  Add  30  c.c. 
of  hot  water  to  the  precipitate,  stir  well,  let  stand  three  or  four 
minutes,  and  again  decant.  Repeat  the  decantation  a  third  time 
and  then  transfer  the  precipitate  to  the  filter  and  wash  about 
eight  times  with  hot  water. 

Reserve  the  filtrate  and  washings  for  the  determination  of 
magnesia. 

Now  run  10  c.c.  of  water  through  the  filter  and  catch  it  in  a 
small  beaker,  add  J-^  c.  c.  sulf uric  acid,  heat  to  70°  and  add  a  drop 
of  standard  permanganate  solution.  If  the  color  is  not  dis- 
charged in  two  or  three  minutes,  the  precipitate  is  sufficiently 
washed;  otherwise  continue  the  washing  and  test  again.  Then 
wash  the  CaC2O4  back  into  the  beaker  in  which  it  was  precipi- 
tated, add  water  if  necessary  to  make  a  volume  of  at  least  150 
c.c.,  place  the  beaker  under  the  funnel  and  run  through  the  filter 
into  the  beaker  30  c.c.  of  1:3  H2SC>4.  Stir  the  contents  of  the 
beaker  thoroughly  while  the  acid  runs  in  to  avoid  the  separation 
of  CaSC>4.  Now  wash  the  funnel  and  filter  thoroughly  with  hot 
water.  Dilute  the  liquid  in  the  beaker  to  350  c.c.,  heat  to  70°C. 
and  titrate  with  permanganate  to  a  faint  pink  color  not  disap- 
pearing in  two  or  three  minutes. 

To  test  the  filter  paper  for  undissolved  CaC204,  it  may  be 
added  to  the  contents  of  the  beaker  and  stirred  up  in  it;  if  the 
washing  has  been  careful,  it  will  not  cause  the  discharge  of  the 
color. 


20  METALLURGICAL  ANALYSIS 

If  the  factor  weight  was  used,  the  number  of  cubic  centimeters 
of  the  permanganate  required  for  the  titration  will  equal  the 
percentage  of  CaCOs  or  CaO  in  the  sample,  for  if  1  c.c.  equals 
0.01  gram  Fe,  it  will  equal  0.00896  gram  CaC03  or  0.00502  gram 
CaO,  and  if  100  c.c.  were  used  it  would  be  equal  to  0.896  gram 
CaCO3  or  0.502  gram  CaO,  which  were  the  samples  to  be  taken. 

The  CaC2O4  obtained  in  the  first  method  given,  instead  of 
being  weighed  as  CaSO4  or  CaO,  may  be  dissolved  and  titrated 
by  permanganate  as  in  the  volumetric  process. 

When  magnesium  is  present  in  considerable  amount  two  pre- 
cipitations of  the  CaC2O4  must  be  made,  for  the  same  reason 
that  two  precipitations  are  required  in  the  gravimetric  process 
when  magnesia  is  high,  i.e.,  because  the  CaC2O4  will  carry  down 
with  it  some  MgC2O4.  If  two  precipitations  are  to  be  made  it  is 
necessary  to  filter  off  theFe(OH)3  separately,  as  it  will  be  reduced 
by  the  oxalic  acid  when  the  CaC2O4  is  dissolved  in  HC1  and  inter- 
fere with  the  magnesia  determination. 

Notes  on  the  Process. — Ignition  of  the  sample  is  necessary  to  destroy 
any  organic  matter  present,  which  if  not  destroyed  will  reduce  KMn04 
and  cause  the  calcium  results  to  run  high. 

Unless  the  precipitate  of  CaC2O4  is  stirred  up  in  a  considerable  vol- 
ume of  water,  when  the  first  few  cubic  centimeters  of  sulf uric  acid  are 
added  to  dissolve  it,  a  dense  flaky  precipitate  of  CaSO4  may  separate 
which  is  likely  to  occlude  solution  and  obscure  the  end  point. 

If  the  KMn04  is  added  too  rapidly  during  the  titration  or  the  solution 
is  not  well  stirred,  brown  MnO2  may  separate  out;  if  this  is  not  redis- 
solved  the  results  will  be  inaccurate. 

All  water  used  in  diluting  the  solutions  in  this  process  for  lime  must 
be  free  from  CO2,  or  CaCOs  will  come  down  with  the  CaC204,  and  as  this 
does  not  react  with  the  permanganate,  the  lime  will  run  low.  For  the 
same  reason  it  is  important  that  all  CO2  be  expelled  from  the  solution  of 
the  sample  in  HC1  by  boiling  it  thoroughly. 

REFERENCES  ON  VOLUMETRIC  DETERMINATION  OF  LIME  AND  MAGNESIA: 
FRESENIUS,  "Quantitative  Analysis." 
BUTTON,  "Volumetric  Analysis." 
HANDY,  J.  Am.  Chem.  Soc.,  1900,  p.  31. 
MEADE,  J.  Am.  Chem.  Soc.,  1899,  p.  746. 
ULKE,  Eng.  Mining  J.,  1900,  LXIX,  p.  164. 
KONNICK,  J.  Soc.  Chem.  Ind.,  1900,  p.  564. 

For  the  conditions  for  the  titration  of  oxalate  by  permanganate  see 
McBRiDE,  J.  Am.  Chem.  Soc.,  1912,  p.  393. 


THE  ANALYSIS  OF  LIMESTONES  21 

THE  DETERMINATION  OF  FREE  LIME 

This  is  based  on  the  fact  that  uncombined  CaO  forms  soluble  com- 
pounds with  sugar  in  solution  in  water  and  that  calcium  carbonate, 
alumina,  ferric  oxide,  magnesium  carbonate  and  free  magnesia  do  not 
dissolve.  The  writer  has  carefully  tested  the  effect  of  the  presence  of 
free  magnesia  upon  this  determination  of  free  lime  and  finds  that  it  is 
without  influence. 

The  method  is  very  convenient  for  the  determination  of  free  lime  in 
burnt  and  hydrated  limes. 

Process  of  Analysis. — Place  1  gram  of  the  finely  ground  sample 
in  a  200  c.c.  flask,  add  15  grams  of  cane  sugar  and  50  c.c.  of  water 
and  shake  the  flask  vigorously  for  several  minutes.  Dilute  to 
the  mark,  mix  the  solution  thoroughly  and  let  the  residue  settle 
until  the  solution  is  clear,  pipette  off  100  c.c.  and  titrate  the  lime 
with  standard  HC1,  using  phenolphthalein  as  indicator.  If  the 
HC1  is  N/5,  each  cubic  centimeter  is  equal  to  0.005607  gram  of 
CaO.  Phenolphthalein  is  prepared  as  directed  on  page  57. 

To  prepare  the  N/5  hydrochloric  acid  proceed  as  follows :  Dilute 
17.0  c.c.  of  HC1,  sp.  gr.  1.19,  to  1  liter  and  standardize  exactly 
as  directed  on  page  57  for  the  standardization  of  HNO3,  except 
that  0.53  gram  Na2CO3  should  be  weighed;  or  ignite  2. 002" grams 
of  pure,  dry,  powdered  Iceland  spar  (CaC03)  in  a  platinum 
crucible  over  a  Meker  burner  until  constant  weight  is  attained, 
dissolve  completely  in  sugar  solution  as  directed  above,  dilute 
to  200  c.c.,  pipette  off  50  c.c.  and  titrate  with  the  acid  to  be 
standardized.  If  the  acid  is  exactly  N/5,  50  c.c.  will  be  required. 
If  the  acid  is  too  strong,  as  it  will  likely  be,  dilute  the  calculated 
amount  and  titrate  again. 

Note. — Hydrochloric  acid  makes  the  best  standard  acid  for  general  use 
because  it  forms  readily  soluble  salts  with  all  the  radicals  commonly 
titrated  with  acids,  is  easily  obtained  pure,  the  strength  of  the  acid  is 
easily  verified  by  means  of  silver  nitrate,  the  dilute  solutions  used  suffer 
no  appreciable  loss  when  boiled,  and  the  strength  of  the  acid  does  not 
change  on  keeping. 

REFERENCES: 

STONE  and  SCHENK,  J.  Am.  Chem.  Soc.,  16,  721. 
WEISBERG,  Chem.  News,  82,  284. 
MELLOR,  "Quantitative  Analysis,"  527. 


CHAPTER  III 
THE  DETERMINATION  OF  IRON  IN  ORES 

Many  iron  ores  give  up  practically  all  of  their  iron  to  hydrochloric 
acid,  provided  that  the  acid  be  strong  and  the  ore  be  very  finely  pulver- 
ized. On  the  other  hand,  many  ores  contain  a  small  amount  of  iron  in 
such  a  state  of  combination  that  it  will  not  dissolve  in  hydrochloric  acid. 
In  such  cases  the  residue  after  treatment  with  acid  must  be  fused  and 
the  iron  determined  in  the  fusion. 

If  the  residue  after  treatment  with  HC1  is  pure  white  with  no  dark 
specks,  the  iron  is  probably  all  dissolved  unless  the  ore  contains  Ti02,  in 
which  case  an  insoluble  compound  of  iron,  titanium  and  phosphorus 
may  remain  which  will  not  color  the  residue. 

Sometimes  previous  ignition  of  the  ore  will  cause  the  ore  to  dissolve 
more  completely  in  acid. 

All  methods  for  the  determination  of  iron  in  ores  depend  upon  reduc- 
ing the  iron  in  acid  solution  to  the  divalent  form,  then  measuring  the 
amount  of  a  standard  oxidizing  agent  required  to  oxidize  the  iron  back 
to  the  trivalent  condition.  The  reducing  agents  are  metallic  zinc, 
metallic  aluminium,  SnCl2,  H2S,  S02.  The  oxidizing  agents  are  K2Cr207 
and  KMn04. 

THE  DETERMINATION  OF  IRON  BY  POTASSIUM  DICHROMATE 

AFTER  REDUCTION  OF  THE  FERRIC  CHLORIDE  BY 

STANNOUS  CHLORIDE 

The  process  depends  upon  the  following  reactions: 

1.  A  strongly  acid  solution  of  FeCl3,  if  boiling  hot,  is  almost  instantly 
reduced  to  FeCl2  by  a  solution  of  SnCl2,  the  end  of  the  reaction  being 
shown  by  the  disappearance  of  the  yellow  color  of  the  ferric  ion. 

2FeCl3+SnCl2  =  2FeCl2+SnCl4. 

2.  Any  slight  excess  of  stannous  chloride  can  be  removed  by  adding 
HgCl2,  forming  a  white  precipitate  of  HgCl  which  is  without  action  on 
iron  salts  or  dichromate,  the  stannous  chloride  being  oxidized  to  stannic 
chloride  by  the  HgCl2. 

SnCl2+2HgCl2  =  SnCl4+2HgCl. 
22 


THE  DETERMINATION  OF  IRON  IN  ORES  23 

The  reaction  is  not  instantaneous,  and  after  the  addition  of  the 
HgCl2  at  least  two  or  three  minutes  should  elapse  before  titration. 
The  reaction  is  satisfactory,  provided  not  too  much  SnCl2  is  present 
and  the  HgCl2  is  in  large  excess  and  added  all  at  once.  Otherwise 
metallic  mercury  may  be  formed  as  a  gray  precipitate  which  will  act 
on  the  dichromate  and  cause  false  results.  Thus,  SnCl2+HgCl2  = 
SnCU+Hg.  This  reaction  is  at  once  detected  by  the  gray  color  of  the 
precipitate  and  entirely  vitiates  the  results.  If  the  solution  is  very  hot 
the  difficulty  of  avoiding  reduction  to  mercury  is  increased. 

3.  When  a  solution  of  potassium  dichromate  is  added  to  a  solution  of 
FeCl2  containing  a  considerable  excess  of  HC1,  the  FeCl2  is  immediately 
oxidized  to  FeCl3  with  a  corresponding  reduction  of  dichromate  to 
CrCla  giving  a  green  color  to  the  solution.     The  reaction  is, 

K2Cr207+ 14HCl+6FeCl2  =  2KCl+2CrCl3+ 6FeCl3+7H2O. 

In  the  absence  of  an  excess  of  HC1  the  solution  becomes  yellowish  in- 
steadof  green,  and  more  HC1  must  be  added,  otherwise  error  will  be  made. 

4.  The  end  point,  that  is,  the  completion  of  the  oxidation,  is  deter- 
mined by  the  use  of  potassium  ferricyanide.     When  a  drop  of  the 
solution  containing  a  ferrous  salt  is  added  to  a  drop  of  a  dilute  solution 
of  ferricyanide  an  intense  blue  color  is  produced,  while  solutions  contain- 
ing only  ferric  salts  give  a  yellow-brown  color  with  ferricyanide.     The 
ferricyanide  solution  must  be  fresh,  as  it  is  reduced  on  exposure  to  light 
or  on  standing,  with  a  formation  of  ferrocyanide,  and  of  course  the  salt 
must  be  pure;  some  ferricyanide  is  contaminated  with  ferrocyanide, 
which  gives  a  blue  color  with  both  ferric  and  ferrous  iron  and  conse- 
quently cannot  be  used. 

Preparation  of  the  Solutions.  1.  Potassium  Dichromate 
Solution. — Place  a  platinum  crucible  containing  a  sufficient 
quantity  of  dichromate  in  a  sand-bath  with  the  sand  as  high  on 
the  outside  as  the  dichromate  on  the  inside  of  the  crucible.  Heat 
until  fusion  of  the  dichromate  just  commences  around  the  sides 
of  the  crucible.  Then  remove  the  crucible. 

Weigh  out  exactly  8.779  grams  of  the  cold  powdered  dichro- 
mate; dissolve  in  300  c.c.  of  cold  water,  transfer  to  a  liter  flask, 
dilute  to  1  liter,  and  shake  well  to  insure  thorough  mixing.  One 
cubic  centimeter  of  this  solution  should  oxidize  exactly  0.01 
gram  of  iron  from  ferrous  to  ferric  condition. 

Now  to  test  the  solution  dissolve  2.81  grams  of  pure  ferrous 
ammonium  sulfate,  (NH4)2Fe(S04)26H2O,  in  75  c.c.  of  water  con- 
taining 7  c.c.  of  HC1.  The  salt  contains  14.24  per  cent.  Fe  and 


24  METALLURGICAL  ANALYSIS 

should  require  just  40  c.c.  of  the  dichromate  solution  to  titrate  it. 
Run  in  from  a  burette  39  c.c.  of  the  dichromate  solution,  stir  well 
and  add  a  drop  of  the  solution  to  a  drop  of  the  ferricyanide  solu- 
tion placed  on  a  white  porcelain  plate.  A  blue  color  forms  if 
ferrous  iron  is  present.  Now  add  the  dichromate  solution  drop 
by  drop,  testing  the  liquid  after  each  addition  until  on  testing 
with  ferricyanide  a  yellow  color  is  produced  instead  of  a  blue 
after  one-half  minute.  If  the  burette  is  properly  calibrated  and 
the  dichromate  properly  made  the  liquid  in  the  burette  should 
now  read  40  c.c.  If  it  does  not,  repeat  the  test  and  make  a  factor 
of  correction.  For  example:  If  instead  of  40  c.c.  of  dichromate 
40.2  were  required,  the  strength  of  the  dichromate  in  terms  of 

40 
iron  would  be  TTToXO.  01  =0.0099502  gram  per  cubic  centimeter. 

For  volume  corrections  see  table  8,  page  325. 

The  object  of  the  heating  of  the  dichromate  is  to  expel  water 
and  destroy  any  trace  of  organic  matter  present. 

If  the  salt  is  strictly  pure  and  the  fusion  has  been  carefully 
conducted  it  will  dissolve  to  a  perfectly  clear  liquid  which  will 
check  exactly  with  the  iron  salt  if  this  is  also  pure.  This  makes 
a  double  check  on  the  solution  and  the  results  obtained  by  the 
two  methods  should  closely  agree.  Of  course  the  burette  used 
must  be  carefully  calibrated. 

Some  of  the  dichromate  on  the  market  contains  excess  of 
chromic  acid,  and  gives  too  strong  a  solution.  When  this  is 
true  the  salt  should  be  purified  by  recrystallization.  If  the  salt 
is  heated  too  hot,  especially  if  it  is  not  pure,  the  solution  will  be 
turbid.  If  more  than  a  trace  of  this  turbidity  shows,  a  new  solu- 
tion should  be  prepared. 

2.  Stannous  Chloride  Solution. — Dissolve  stannous  chloride  in 
four  times  its  weight  of  a  mixture  of  three  parts  of  water  and  one 
of  HC1,  sp.  gr.  1.2.     Add  scraps  of  metallic  tin  and  boil  until  the 
solution  is  clear.     Keep  this  solution  in  a  closed  dropping  bottle 
containing  metallic  tin. 

3.  Saturated  Solution  of  Mercuric  Chloride. — Keep  an  excess 
of  salt  in  a  bottle  and  fill  it  up  with  water  from  time  to  time. 

4.  A  Very  Dilute  Solution  of  Potassium  Ferricyanide. — Dis- 
solve a  piece  half  as  big  as  a  small  pea  in  50  c.c.  of  water.     This 
solution  must  be  made  fresh  when  wanted  as  it  does  not  keep. 


THE  DETERMINATION  OF  IRON  IN  ORES  25 

The  other  solutions  keep  indefinitely.  The  SnCl2  solution, 
however,  absorbs  oxygen  from  the  air  and  hence  must  be  kept 
closed.  Should  it  grow  turbid  or  deposit  a  white  precipitate, 
add  more  HC1  and  metallic  tin  and  heat  until  clear. 

Process  for  the  Analysis. — Pulverize  the  ore  in  an  agate  mor- 
tar until  it  is  so  fine  that  no  grit  can  be  felt  between  the  teeth. 
It  is  best  to  grind  a  small  amount  at  a  time. 

Weigh  out  1  gram;  put  it  into  a  small  dry  beaker,  brushing  off 
the  watch-glass  carefully.  Add  25  c.c.  HC1,  sp.  gr.  1.2,  cover  the 
beaker  with  a  watch-glass  and  set  it  on  a  hot  plate.  Digest  at  a 
temperature  just  short  of  boiling  until  all  iron  is  dissolved  and 
on  shaking  the  beaker  the  residue  appears  light  and  flotant,  and 
free  from  dark  heavy  particles.  This  may  take  from  15  minutes 
to  an  hour  or  more  according  to  the  nature  of  the  ore.  Dilute 
the  solution  to  two  or  three  times  its  original  volume,  filter 
through  a  small  filter  into  a  250  c.c.  beaker,  and  wash  the  residue 
on  the  filter  until  it  is  free  from  acid.  Heat  the  solution  to 
boiling,  drop  in  the  tin  solution  slowly  until  the  last  drop  makes 
the  solution  colorless,  indicating  complete  reduction.  If  too 
much  stannous  chloride  is  dropped  in  by  mistake,  add  per- 
manganate to  the  solution  until  a  yellow  color  appears,  then 
again  add  stannous  chloride  drop  by  drop  until  the  yellow  just 
disappears.  Dilute  with  cold  water  to  200  c.c.,  then  add  all  at 
once,  with  vigorous  stirring,  15  c.c.  of  the  mercuric  chloride  solu- 
tion. Let  stand  three  or  four  minutes.  A  slight  white  precipi- 
tate should  form.  If  none,  or  a  heavy  grayish  precipitate  forms, 
the  result  is  rendered  doubtful  and  the  determination  should  be 
repeated. 

Divide  the  solution  into  halves  approximately.  Into  one-half 
run  in  the  standard  dichromate  solution  until  the  end  point  is 
roughly  obtained,  then  add  the  other  half,  washing  the  solution 
out  of  the  beaker  thoroughly  and  complete  the  titration  accu- 
rately. The  final  end  point  is  known  approximately  from  the  end 
point  obtained  on  the  first  half  of  the  solution.  In  this  way  it  is 
not  necessary  to  consume  much  time  approaching  the  end  point. 
The  number  of  cubic  centimeters  used  multiplied  by  the  iron 
factor  of  the  dichromate  and  then  by  100  gives  the  percentage  of 
iron  in  the  sample. 

If  by  any  accident  too  much  of  the  dichromate  solution  is  run 


26  METALLURGICAL  ANALYSIS 

in,  add  1  c.c.  of  a  dilute  solution  of  ferrous  sulfate,  finish  the 
titration  and  read  the  burette.  Then  add  1  c.c.  more  of  the 
same  solution,  again  finish  the  titration  and  read  the  burette. 
Deduct  the  difference  between  the  first  and  second  readings  from 
the  first  reading  to  find  the  true  end  point. 

Notes  on  the  Process. — When  an  ore  is  with  difficulty  decomposed 
by  HC1,  the  addition  of  2  or  3  c.c.  of  SnCl2  solution  to  the  ore  and  acid 
in  the  beaker  will  greatly  accelerate  the  solution  of  the  ore.  In  this 
case,  after  the  color  and  nature  of  the  residue  shows  complete  extrac- 
tion, carefully  add  a  solution  of  KMnO4  to  the  contents  of  the  beaker 
until  the  yellow  color  of  ferric  chloride  again  appears,  then  dilute  and 
proceed  as  usual.  The  object  of  the  permanganate  is  to  oxidize  the 
excess  of  stannous  chloride. 

In  the  case  of  unknown  ores,  or  of  an  ore  in  which  not  all  of  the  iron 
can  be  completely  dissolved  by  HC1,  the  residue  after  solution  in  HC1 
must  be  fused  to  render  soluble  the  rest  of  the  iron.  Place  the  filter  in 
a  platinum  crucible,  burn  off  the  paper,  add  2  or  3  grams  of  KHS04  and 
fuse  over  a  Bunsen  burner  until  all  iron-  is  extracted.  Dissolve  the 
fusion  in  50  c.c.  of  water  and  5  c.c.  of  HC1,  heat  to  boiling,  add  a  drop 
of  stannous  chloride  solution  and  then  place  a  drop  of  the  solution  on  a 
white  plate  and  test  for  ferric  iron  with  KCNS.  If  a  red  color  is  pro- 
duced more  stannous  chloride  is  needed,  but  the  chances  are  that  not 
more  than  one  drop  of  stannous  chloride  will  be  required.  The  reason 
for  using  KCNS  is  that  after  fusion  in  platinum  some  platinum  always 
goes  into  solution,  and  stannous  chloride  produces  with  this  a  yellow 
color,  so  that  the  end  of  the  reduction  cannot  be  told  by  the  disappear- 
ance of  the  yellow  color  of  ferric  chloride. 

Now  add  HgCl2  and  titrate  as  in  the  case  of  the  main  solution. 

There  is  danger  of  loss  of  iron  if  a  concentrated  solution  of  FeCl3  in 
HC1  is  boiled;  hence  too  great  concentration  of  the  solution  and  too  hard 
boiling  must  be  avoided. 

In  testing  the  solution  to  see  if  the  end  point  is  near,  care  should  be 
used  that  only  very  small  drops  of  the  solution  which  is  being  titrated 
are  removed,  otherwise  an  appreciable  amount  of  untitrated  iron  may 
be  taken  out,  causing  low  results.  As  the  end  point  is  approached  the 
blue  color  obtained  when  the  test  is  made  with  ferricyanide  grows  less 
intense  until  the  addition  of  one  more  drop  of  dichromate  to  the  iron 
solution  gives  a  test  with  no  trace  of  green  color. 

In  the  case  of  mill  cinder  and  other  decomposable  slags,  add  20  c.c. 
of  water  to  the  finely  powdered  material,  and  stir  up  well  to  prevent 
the  cinder  caking  on  the  bottom  of  the  beaker;  then  add  25  c.c.  HC1  and 
proceed  as  before. 


THE  DETERMINATION  OF  IRON  IN  ORES  27 

Titanium  will  not  affect  this  process,  provided  care  be  taken  to  fuse 
the  residue  and  add  the  solution  of  the  fusion  to  the  main  solution. 
When  zinc  is  used  to  reduce  the  iron,  titanium  is  also  partly  reduced. 

The  presence  of  vanadium  will  vitiate  the  results  as  it  is  reduced  by 
SnCl2  and  oxidized  by  dichromate. 

The  porcelain  plate  upon  which  the  tests  for  the  end  point  are  made 
should  be  prepared  by  warming  a  plate  on  a  steam-bath,  then  rubbing 
with  a  piece  of  paraffin  so  as  to  cover  the  whole  plate  with  a  thin  skin 
of  paraffin.  The  test  drops  will  not  then  spread  over  the  plate. 


THE   DETERMINATION   OF  IRON  BY   TITRATION  BY   POTASSIUM 
PERMANGANATE  AFTER  REDUCTION  BY  METALLIC  ZINC 

This  is  a  widely  used  process.  The  time  of  the  actual  titration  is 
shorter  than  with  the  dichromate,  as  an  outside  indicator  is  unnecessary 
because  the  permanganate  acts  as  its  own  indicator.  The  least  bit  of 
permanganate  added  to  the  solution  in  excess  of  that  required  to 
titrate  it  gives  to  the  solution  a  permanent  pink  color. 

On  the  other  hand,  the  permanganate  is  much  more  liable  to  change 
than  the  dichromate  and  is  also  much  more  subject  to  reduction  by 
other  materials,  as  for  example,  organic  matter  in  the  ore  or  solution. 

Titration  by  permanganate  in  HC1  solution  is  only  permissible  under 
certain  closely  regulated  conditions.  The  amount  of  HC1  must  be 
small  and  a  certain  amount  of  manganese  salt  must  be  present,  other- 
wise the  HC1  will  cause  some  reduction  of  the  permanganate,  giving  a 
brown  color  to  the  solution  and  making  the  results  run  too  high.  The 
presence  of  phosphoric  acid  is  desirable  as  it  changes  the  yellow  ferric 
chloride  to  colorless  ferric  phosphate,  thus  making  the  end  point  plainer. 
The  phosphoric  acid  is  also  said  to  prevent  the  reduction  of  permanganate 
by  the  HC1. 

Reduction  of  the  iron  by  zinc  is  accomplished  either  by  adding  granu- 
lated zinc  to  the  solution  in  an  Erlenmeyer  flask  and  boiling  a  few 
minutes  or  by  using  the  "reductor"  introduced  by  Mr.  Clemens  Jones, 
in  which  the  iron  solution  is  filtered  through  a  column  of  amalgamated 
granulated  zinc. 

Zinc  is  such  a  powerful  reducing  agent  that  many  substances  are 
reduced  by  it  to  oxidizable  forms  which  vitiate  the  result.  Thus  the 
iron  solution  must  not  contain  arsenic,  titanium,  vanadium,  or  nitrates, 
since  lower  oxides  are  formed  which  are  oxidized  by  permanganate. 
Nitrates  are  reduced  ultimately  to  ammonia  which  does  no  harm,  but 
frequently  the  reduction  is  only  partial  resulting  in  the  formation  of 
hydroxylamine  (NH2OH)  which  is  oxidized  by  permanganate.  The 


28  METALLURGICAL  ANALYSIS 

writer  has  known  of  results  for  iron  running  as  high  as  125  per  cent, 
because  the  H2S04  used  had  in  it  HN03  which  was  reduced  to  NH2OH. 

As  the  zinc  is  never  pure,  a  blank  must  be  run  on  it  and  the  amount 
obtained  subtracted  from  the  permanganate  used  in  the  regular  titra- 
tion.  If  pure  zinc  is  used  without  being  amalgamated  with  mercury 
the  zinc  used  must  be  completely  dissolved  each  time  as  it  reduces  some 
iron  on  it  as  metallic  iron,  making  the  result  run  low.  When  the  zinc 
is  amalgamated  the  reduction  is  much  less  powerful,  in  fact  if  the  mer- 
cury coating  is  too  heavy  the  reduction  of  the  iron  is  apt  to  be  too  slow. 
There  should  be  not  more  than  5  per  cent,  free  acid  present. 

The  reactions  involved  are:  Zn  +  Fe2(SO4)3  =  ZnS04  +  2FeS04. 
2KMnO4+10FeS04+8H2S04  =  K2S04+2MnSO4+5Fe2(S04)3+8H20. 

Solution  Required.  Permanganate  Solution. — A  convenient 
solution  is  one  in  which  1  c.c.  equals  0.01  gram  of  iron,  i.e.,  one 
which  has  in  1  c.c.  sufficient  permanganate  to  oxidize  0.010  gram 
of  iron  from  divalent  to  trivalent  condition.  This  will  contain 
5.659  gram  of  KMn04  to  the  liter. 

To  prepare  the  solution,  dissolve  5.7  grams  of  pure  permanga- 
nate of  potassium  in  water,  and  when  dissolved  dilute  to  1  liter. 
The  solution  should  stand  a  day  or  so  before  being  standardized. 
It  is  likely  to  alter  rapidly  at  first,  but  in  time  reaches  a  com- 
paratively stable  condition  if  protected  from  light  and  dust. 
Where  large  quantities  are  used  it  is  a  good  plan  to  make  up  a 
carboy  ahead  and  let  it  be  "ageing."  The  container  should  be 
painted  black  to  keep  out  light. 

Standardization  of  the  Permanganate. — The  reducing  reagents 
used  as  standards  are:  Pure  iron  wire,  ferrous  ammonium  sul- 
fate,  sodium  oxalate  and  oxide  of  iron  or  iron  ore  in  which  the 
iron  content  is  known.  It  is  best  to  standardize  against  several 
of  these  reagents  and  the  results  should  agree  closely.  If  they 
do  not,  purer  materials  should  be  obtained. 

To  standardize  against  iron  wire  proceed  as  follows:  Clean 
the  wire  by  rubbing  it  with  emery  cloth  and  then  with  filter 
paper.  Form  it  into  a  spiral  by  wrapping  it  around  a  clean  glass 
rod  and  cut  the  spiral  into  lengths  weighing  about  0.4  gram. 
Throw  away  the  part  of  the  wire  which  was  held  by  the  fingers. 
Accurately  weigh  the  pieces  and  put  them  into  small  Erlenmeyer 
flasks  of  about  75  c.c.  capacity.  Close  each  flask  by  a  small  glass 
bulb  with  the  stem  reaching  down  into  each  neck.  The  glass  bulb 


THE  DETERMINATION  OF  IRON  IN  ORES  29 

prevents  air  entering  the  flask  and  oxidizing  the  iron.  Add  30  c.c. 
of  H2S04  (1:4)  and  set  the  flask  on  a  hot  plate  until  the  iron 
dissolves,  avoiding  violent  boiling.  When  the  iron  is  completely 
dissolved,  pour  cold  water  over  the  bulb  into  the  flask,  thus  wash- 
ing both  the  bulb  and  the  neck  of  the  flask.  Transfer  the  solu- 
tion to  a  beaker,  dilute  to  200  c.c.  and  titrate  without  delay. 
The  weight  of  the  wire  taken  multiplied  by  the  iron  factor  of  the 
wire  and  divided  by  the  number  of  cubic  centimeters  of  the  per- 
manganate used  will  be  the  amount  of  iron  equivalent  to  1  c.c.  of 
the  permanganate.  The  result  may  be  checked  by  running  the 
titrated  solution  through  the  reductor  and  again  titrating.  With 
the  " blank"  deducted,  the  results  ought  to  check.  The  wire  is 
usually  about  99.8  per  cent.  iron. 

Now,  knowing  the  strength  of  the  solution  it  may  be  diluted  so 
that  1  c.c.  will  just  equal  0.0100  gram  of  iron.  The  water  used 
for  diluting  should  have  been  boiled  and,  while  boiling,  treated 
with  permanganate  until  it  retains  a  very  faint  pink  color. 

In  all  work  involving  the  use  of  permanganate,  glass  stop- 
cocked  burettes  should  be  used,  as  it  is  reduced  by  rubber. 

To  standardize  with  ferrous  ammonium  sulfate  or  sodium 
oxalate,  weigh  2.81  grams  of  the  sulfate  or  0.4799  gram  of  the 
oxalate,  transfer  to  a  300  c.c.  flask,  add  250  c.c.  of  hot  water 
containing  8  c.c.  of  strong  H2SO4  and  titrate  not  too  rapidly, 
approaching  the  end  point  slowly.  In  the  case  of  the  oxalate  the 
titration  should  be  carried  on  at  70°C. 

The  amounts  of  sulfate  and  oxalate  given  above  are  each  equal 
to  0.400  gram  of  iron.  The  reason  this  amount  is  chosen  is  that 
it  is  about  the  amount  of  iron  that  will  ordinarily  be  titrated  in  a 
sample  of  ore  and  consequently  no  end-point  correction  will  have 
to  be  made.  The  end  color  obtained  in  standardization  should 
be  of  the  same  depth  as  when  a  sample  of  ore  is  titrated. 

2.  Titrating  Solution. — This  is  made  by  dissolving  160  grams 
of  manganous  sulfate  in  water,  diluting  to  1750  c.c.,  adding  330 
c.c.  of  phosphoric  acid  and  320  c.c.  of  sulfuric  acid.  Use  the  con- 
centrated "Byrupy  phosphoric  acid"  of  1.725  sp.  gr. 

Preparation  of  the  Reductor. — A  simple  form  of  the  reductor  is 
shown  in  Fig.  3.  The  large  tube  is  about  %  in.  inside  diameter 
and  is  contracted  at  the  bottom  and  expanded  into  a  funnel  at 
the  top.  The  stem  enters  the  rubber  stopper  of  the  flask,  which 


30 


METALLURGICAL  ANALYSIS 


is  connected  to  a  suction  pump.  The  tube  is  filled  as  follows :  A 
plug  of  glass  wool  is  placed  in  the  bottom.  Above  this  is  %  in. 
of  clean  white  sand  B,  which  has  been  boiled  with  HC1  and  then 
washed  to  remove  the  iron.  Above  the  sand  is  a  disc  of  perfor- 
ated platinum  C.  Above  this  the  tube  is  filled  for  10  in.  with 
granulated  zinc  of  such  size  that  it  will  pass  through  a  20-mesh 
sieve  but  not  through  a  30-mesh.  It  should  be  amalgamated  as 
follows :  Moisten  a  quantity  of  it  with  very 
dilute  H2SO4  (about  3  c.c.  to  100  c.c.  of 
water),  add  a  small  drop  of  mercury  and 
stir  it  in  until  the  zinc  shows  uniformly 
the  white  mercury  color.  Wash  the  zinc 
free  from  acid  and  put  it  in  the  tube. 
Avoid  more  than  just  enough  mercury. 
One-half  gram  is  sufficient  for  150  grams 
of  zinc. 

The  solution  to  be  reduced  is  poured  into 
the  funnel-shaped  top  of  the  reductor. 
The  rate  at  which  it  is  drawn  through  must 
not  be  too  rapid.  Test  this  point  by  draw- 
ing an  iron  solution  through  and  then  add- 
ing some  ammonium  sulfocyanate  to  the 
reduced  solution.  If  this  gives  a  pink  color 
the  speed  was  too  great  and  must  be  re- 
duced by  diminishing  the  suction.  If  the 
rate  is  too  fast  it  can  be  reduced  by  open- 
ing the  pinch-cock.  If  air  is  drawn  through 
the  zinc  in  the  reductor  and  immediately 

followed  by  dilute  acid,  the  liquid  running  through  is  sometimes 
found  to  be  oxidizing,  possibly  from  the  formation  of  H2O2; 
hence  while  running  through  the  solution  and  wash  water,  the 
surface  of  the  zinc  must  be  kept  continually  covered  with  liquid. 
If  the  reductor  has  stood  unused  for  some  time  it  should  be 
washed  out  with  dilute  sulfuric  acid  and  water  before  putting  the 
solution  through  it. 

Process  of  Analysis. — Weigh  out  1  gram  of  the  finely  ground 
sample  and  ignite  it  in  a  porcelain  crucible  to  destroy  organic 
matter.  Transfer  it  to  a  small  beaker,  add  10  c.c.  of  concentrated 
HC1,  cover  and  digest  till  all  the  iron  is  in  solution.  Add  20  c.c. 


FIG.  3. 


THE  DETERMINATION  OF  IRON  IN  ORES  31 

of  dilute  H2S04  (1:1)  and  boil  gently  to  expel  some  of  the  excess 
of  HC1,  then  dilute  to  about  100  c.c.  and  filter,  washing  the  residue 
thoroughly.  Dilute  the  filtrate  to  250  c.c.,  using  cold  water,  as 
the  solution  should  be  cool. 

Now  pour  the  solution  into  the  zinc  reductor  and  apply  such 
suction  that  the  liquid  will  flow  through  in  a  moderate  stream. 
Follow  the  solution  with  100  c.c.  of  5  per  cent.  H2S04,  then  with 
150  c.c.  of  water,  keeping  the  zinc  covered  with  liquid  during  the 
entire  process  so  that  air  will  not  be  drawn  through  the  zinc.  As 
soon  as  the  last  wash  water  has  passed  through,  disconnect  the 
suction  tube,  pour  the  solution  into  a  large  beaker  and  rinse  the 
flask  out  with  a  little  water.  Add  10  c.c.  of  the  titrating  solution 
and  titrate  with  KMnO4.  The  number  of  cubic  centimeters  of 
the  KMnO4  times  the  iron  factor,  times  100  equals  the  percentage 
of  iron. 

Notes  on  the  Process. — Ignition  of  the  sample  is  necessary  unless 
organic  matter  is  known  to  be  absent. 

The  gentle  boiling,  after  adding  the  dilute  H2S04  gets  rid  of  most  of 
the  HC1.  It  is  not  necessary  to  expel  all  of  it. 

Determine  the  correction  of  the  impurity  in  the  zinc  by  running  a 
blank  with  the  same  amount  of  water  and  acids  used  in  the  analysis, 
and  deduct  the  volume  of  permanganate  required  in  this  from  that  used 
in  the  analysis. 

The  process  should  be  checked  on  ores  of  known  composition. 

THE  PERMANGANATE  METHOD  WITH  REDUCTION  BY  STANNOUS 

CHLORIDE 

This  method  is  reliable  provided  the  conditions  of  titration  are 
strictly  controlled.  A  very  slight  excess  of  SnCl2  must  be  used,  the 
amount  of  HC1  present  must  not  be  more  than  is  directed,  the  solution 
to  be  titrated  must  be  cold  and  dilute.  In  strongly  acid  solutions 
HgCl  and  HC1  are  acted  upon  by  permanganate.  The  permanganate 
should  not  be  added  too  rapidly,  especially  toward  the  end.  Organic 
matter  and  sulfides  must  be  destroyed  by  ignition  of  the  ore. 

Process  of  Analysis. — Weigh  1  gram  of  the  finely  ground  ore, 
transfer  it  to  a  crucible  and  ignite  to  redness.  Transfer  to  a 
beaker,  add  20  c.c.  of  HC1  (1  :1).  Heat  until  the  iron  is  all  dis- 
solved. To  hasten  the  solution,  SnCl2  may  be  added  at  this 
point  until  the  solution  becomes  colorless.  Now  if  an  excess  of 


32  METALLURGICAL  ANALYSIS 

SnCl2  has  been  added,  add  permanganate  until  the  yellow  color 
of  ferric  iron  appears,  then  to  the  hot  solution  very  carefully  add 
SnCl2  solution  until  the  yellow  just  disappears.  Cool  thoroughly, 
add  10  c.c.  of  saturated  HgCl2  solution,  stir  well  and  allow  to 
stand  for  several  minutes.  Dilute  to  250  c.c.  with  water  free 
from  reducing  matter,  add  10  c.c.  of  the  "titrating  solution," 
and  titrate  not  too  rapidly  with  permanganate.  Approach  the 
end  point  rather  slowly.  The  last  drop  should  give  a  persistent 
pink  color. 

Note. — Instead  of  using  SnCl2,  zinc,  aluminum,  or  S02  can  be 
used  to  reduce  the  iron,  and  then  according  to  Hough,  the  only 
reagent  necessary  to  add  to  make  the  titration  accurate  is  phos- 
phoric acid. 

REFERENCES  ON  THE  DETERMINATION  OF  IRON: 

MIXER  and  DUBOIS,   "Permanganate  and  Tin,"  Eng.  Mining  J., 

Vol.  LVII,  p.  342. 

DUDLEY,  "Description  of  Reductor,"  J.  Am.  Chem.  Soc.,  1893,  p.  520. 
SHIMER,  "Description  of  Reductor,"  J.  Am.  Chem.  Soc.,  1899,  p.  723. 
McKENNA,  "Amalgamation  of  Zinc,"  "Methods  of  Iron  Analysis," 

p.  113. 
SEAMON,  "Use  of  Aluminium  for  the  Reduction  of  Iron,"  Western 

Chem.  Met.,  IV,  105. 
TREADWELL-HALL,  "Analytical  Chemistry,"  Vol.  II,    2nd  edit.,  p. 

477,  et  seq. 

JONES  and  JEFFERY,  "Estimation  of  Iron  by  Potassium  Permanga- 
nate in  Presence  of  Hydrochloric  Acid,"  Analyst,  XXXIV,  306. 
"Titration  of  Ferrous  Salts  in  Presence  of  HC1  and  H3PO4,"  J.  Am. 

Chem.  Soc.,  XXXII,  539. 
CAMP,  "Methods  of  Sampling  and  Analysis  of  Iron  Ores,"  J.  Ind. 

and  Eng.  Chem.,  Vol.  I,  No.  2,  p.  107. 

DETERMINATION  OF  FERROUS  OXIDE  IN  IRON  ORE 

This  determination  is  not  frequently  called  for,  but  in  the  case  of 
carbonate  ore,  FeC03 — or  magnetite  ore,  Fe3O4 — it  is  sometimes 
necessary  in  order  to  calculate  the  heat  balance  of  a  blast  furnace. 
The  ferrous  oxide  is  also  determined  to  test  the  completeness  of  calci- 
nation of  carbonate  ore. 

When  ores  of  iron  are  dissolved  in  HC1,  ferric  oxide  goes  in  solution 
as  FeCl3  while  ferrous  oxide  or  ferrous  carbonate  go  in  solution  as  fer- 
rous chloride.  Thus: 

FeC03+2HCl  =  FeCl2+H20+CO2. 
The  FeCl2  can  then  be  titrated  by  any  of  the  ordinary  methods. 


THE  DETERMINATION  OF  IRON  IN  ORES  33 

An  accurate  determination  of  ferrous  oxide  can  be  made  only  when 
certain  possible  constituents  of  ores  are  absent.  Some  organic  material, 
and  all  decomposable  sulfides,  will  reduce  ferric  to  ferrous  iron  and  cause 
the  results  to  run  high.  On  the  other  hand  any  MnC>2,  such  as  pyrolu- 
site,  will  liberate  chlorine  when  the  ore  is  dissolved  in  HC1  and  this  will 
oxidize  the  ferrous  iron  to  ferric,  making  the  results  for  FeO  low. 

Process  of  Analysis. — Fit  a  150  c.c.  flask  with  a  clean  rubber 
stopper  perforated  with  one  hole,  in  which  is  inserted  a  piece  of 
glass  tubing  2  in.  long.  Upon  this  slip  a  piece  of  pure  gum  tubing 
3  in.  long  closed  at  one  end  with  a  glass  rod.  In  the  space  be- 
tween the  tube  and  rod  make  a  vertical  slit  J^  in.  long  with  a 
sharp  knife.  This  acts  as  a  valve  which  keeps  out  the  air  and 
yet  lets  out  the  evolved  gases.  It  is  necessary  to  keep  out  the  air 
to  prevent  it  from  oxidizing  any  ferrous  iron. 

Put  in  the  flask  1  gram  of  Na2CO3  and  add  HC1  at  such  a  rate 
that  the  liquid  will  not  froth  out  of  the  flask.  When  the  carbon- 
ate is  all  dissolved,  place  the  stopper  in  the  flask.  Weigh  out 
1  gram  of  finely  ground  ore,  transfer  to  the  flask,  add  a  small 
pinch  of  carbonate,  and  then  25  c.c.  of  strong  HC1.  Quickly 
insert  the  stopper  and  heat  to  boiling,  and  keep  at  a  boiling  tem- 
perature until  the  ore  is  dissolved.  Add  200  c.c.  of  oxygen-free 
water  and  titrate  with  standard  dichromate  solution.  The  iron 
value  of  the  dichromate  multiplied  by  1.2866  gives  the  amount 
of  FeO  in  the  ore. 


CHAPTER  IV 

THE  DETERMINATION  OF  PHOSPHORUS  IN  IRON  ORES, 
IRON  AND  STEEL 

The  methods  in  general  use  all  depend  upon  first  getting  the  phos- 
phorus into  solution,  as  orthophosphoric  acid,  and  then  separating  it 
from  the  iron  and  other  bases  in  the  form  of  ammonium  phosphodo- 
decamolybdate,  the  so-called  "  yellow  precipitate." 

The  phosphorus  in  this  is  then  determined  directly  or  indirectly,  and 
either  gravimetrically  or  volu  metrically. 

This  substance,  when  dried  at  130°C.,  has  uniformly  the  composition 
(NH4)3PO412MoO3.  This  formula  requires  1.65  per  cent,  of  phosphorus. 
The  average  of  many  most  carefully  conducted  experiments  has  shown 
that  the  precipitate,  if  free  from  admixed  molybdic  acid  or  other  im- 
purities, contains  1.63  per  cent,  phosphorus  within  very  narrow  limits. 

The  precipitate  is  only  obtained  pure  when  formed  under  very  exact 
conditions,  and  is  easily  affected  by  subsequent  treatment,  so  that  all 
methods  depending  upon  the  weighing  of  the  yellow  precipitate  or 
its  volumetric  determination  must  be  carried  out  rigorously  according  to 
the  prescribed  directions  in  every  detail. 

When  a  solution  of  ammonium  molybdate  in  nitric  acid  is  added  to  an 
acid  solution  containing  phosphoric  acid,  the  whole  of  the  phosphoric 
acid  is  precipitated  as  the  yellow  ammonium  phosphomolybdate,  under 
the  following  conditions: 

1.  All  the  phosphorus  must  be  present  as  tribasic  (ortho)  phosphoric 
acid. 

2.  A  decided  excess  of  ammonium  nitrate  or  sulfate  should  be  present. 
The  precipitation  is  most  rapid  when  the  solution  contains  between 

5  and  10  per  cent,  of  the  salt. 

3.  A  certain  excess  of  free  acid  must  be  present — preferably  nitric 
or  sulfuric.     This  must  amount  to  at  least  25  molecules  of  acid  for 
each  molecule  of  P205  present,  and  must  be  increased  when  sulfates  are 
present. 

4.  Too  great  an  excess  of  free  acid  must  be  avoided,  as  this  causes 
decomposition  and  partial  re-solution  of  the  precipitate.     This  action 
becomes  perceptible  when  over  80  molecules  of  acid  are  present  to  each 
molecule  of  P205.     The  concentration  of  the  acid  is  also  important; 
the  smaller  the  volume  of  liquid  the  less  free  acid  must  be  present. 

34 


DETERMINATION  OF  PHOSPHORUS  35 

This  solvent  action  of  free  acid  is  prevented  by  a  sufficient  excess  of 
molybdic  acid  solution,  which  excess  must  be  greater  as  the  amount  of 
free  acid  is  greater.  It  is  also  largely  overcome  by  a  considerable  excess 
of  ammonium  nitrate. 

5.  The  yellow  precipitate  is  insoluble  in  the  solution  of  ammonium 
molybdate  in  nitric  acid;  also  in  solutions  of  ammonium  salts,  if  neutral 
or  only  very  slightly  acid,  but  if  strongly  acid  they  attack  the  precipi- 
tate, which  is,  however,  reprecipitated  by  the  addition  of  molybdic  acid 
solution  to  the  liquid.     It  is  also  practically  insoluble  in  a  solution  of 
potassium  nitrate  when  neutral  and  not  too  dilute.     Solutions  of  salts 
of  organic  acids  usually  dissolve  the  precipitate  to  some  extent.     From 
these  solutions  nitric  acid  and  ammonium  nitrate,  in  some  cases,  re- 
precipitate  the  compound,  in  others,  e.g.,  with  tartaric  acid  or  oxalic 
acid,  probably  not  completely. 

The  mineral  acids,  HC1,  HN03,  H2SO4,  all  have  a  solvent  action  on 
the  precipitate  even  in  the  presence  of  ammonium  nitrate.  HNOs  has 
the  least,  HC1  probably  the  most. 

Pure  water  is  said  to  decompose  the  precipitate  to  a  slight  extent  and 
make  it  run  through  the  filter.  This  is  doubtful,  however. 

6.  Precipitation  is  much  more  rapid  from  hot  than  from  cold  solutions 
but  in  time  it  is  probably  complete  at  any  temperature.     The  pre- 
cipitate from  hot  solutions  is  denser  and  more  crystalline;  from  cold, 
finer  and  more  granular,  and  harder  to  filter  and  wash. 

7.  Agitation  greatly  accelerates  precipitation  in  this  as  well  as  in 
other  chemical  reactions. 

8.  The  precipitate  dried  to  constant  weight  at  ordinary  temperatures 
retains  a  little  acid  and  water,  which  it  loses  when  dried  at  130°C.     By 
washing  the  precipitate  with  a  neutral  solution  of  ammonium  or  potas- 
sium nitrate  or  by  prolonged  washing  with  water,  it  can  be  freed  from 
acid  without  drying. 

9.  Silicic  acid  in  the  solution  does  not  seem  to  interfere  with  the  com- 
plete precipitation  of  phosphorus  as  yellow  precipitate,  but  a  trace  of  the 
SiC>2  usually  comes  down  with  the  precipitate,  especially  if  the  solution 
is  too  concentrated  or  too  warm,  or  stands  too  long.     If  the  solution  is 
rather  dilute,  not  too  hot,  and  is  filtered  promptly  the  yellow  precipi- 
tate can  be  obtained  in  the  presence  of  considerable  SiO2  and  prac- 
tically free  from  it.     Titanic  acid  does  not  prevent  though  it  greatly 
delays  the  precipitation  of  phosphorus  by  molybdic  acid  solution. 

10.  Organic  matter  has  usually  been  supposed  to  interfere  with  the 
precipitation  of  phosphorus,  but  it  is  probable  that  in  many  cases, 
noticeably  in  steel  analysis,  the  bad  results  attributed  to  this  cause  were 
due  to  the  fact  that  the  phosphorus  had  not  all  been  converted  into  the 


36  METALLURGICAL  ANALYSIS 

tribasic  acid.     The  pyro-  and  meta-phosphoric  acids  are  not  completely 
precipitated  by  molybdic  acid  solution. 

11.  When  arsenic  acid  is  present  in  the  solution  with  the  phosphorus, 
some  of  it  will  be  precipitated  at  the  same  time,  the  amount  increasing 
with  the  temperature.     Only  very  small  amounts  come  down  at  tem- 
peratures not  exceeding  25°C. 

12.  Mo03  may  separate  with  the  yellow  precipitate  as  a  light  crystal- 
line deposit.     This  free  MoO3  is  soluble  in  acids  with  difficulty  and  can- 
not be  washed  out  of  the  yellow  precipitate.     Its  separation  must 
always  be  guarded  against  when  the  yellow  precipitate  is  to  be  weighed 
or  titrated.     It  forms  when  the  solution  contains  too  much  MoOa,  is  too 
concentrated,  or  too  dilute,  too  strongly  acid  or  too  nearly  neutral. 
Too  high  a  temperature  precipitates  it.     The  addition  of  strong  nitric 
acid  to  a  solution  of  molybdic  acid  will  sometimes  precipitate  it,  as  will 
the  adding  of  molybdic  acid  solution  to  solutions  of  iron  in  concentrated 
nitric  acid.     Long  standing  favors  the  separation  of  excess  MoOa  with 
the  yellow  precipitate.     A  finely  divided  form  of  the  Mo03  sometimes 
separates,  easily  mistaken  for  the  yellow  precipitate  and  liable  to  escape 
notice. 

13.  Besides  the  Mo03,  the  yellow  precipitate  may  be  contaminated 
by  ferric  molybdate  or  ammonium  tetramolybdate,  which  are  precipi- 
tated by  too  long  digestion  or  too  high  temperature.     If  the  precipitate 
stands  at  a  temperature  not  exceeding  40°C.  contamination  in  this  way 
is  not  apt  to  occur. 

14.  When  the  yellow  precipitate  is  thrown  down  in  a  solution  con- 
taining much  iron  and  not  sufficient  acid,  basic  iron  salts  are  likely  to 
accompany  it,  making  it  reddish  in  color.     This  is  especially  the  case 
when  the  solutions  are  hot. 

15.  The  yellow  precipitate,  if  pure,  is  easily  and  completely  sol- 
uble in  ammonia  (if  it  contains  iron,  the  solution  will  be  turbid  from 
the  formation  of  ferric  phosphate).     From  this  solution  the  phosphoric 
acid  is  completely  precipitated  by  magnesia  mixture  as  MgNH4PO4. 
If  the  yellow  precipitate  contains  any  SiO2,  this  will  also,  in  part  at 
least,  dissolve  in  the  ammonia  and  separate  with  the  magnesia  precipi- 
tate, making  it  a  little  flocculent.     By  cautiously  adding  HC1  to  the 
ammonia  solution  of  the  yellow  precipitate  until  nearly  neutral  and 
letting  it  stand  for  some  time  in  a  warm  place,  the  silica  separates  and 
may  be  filtered  off.     The  phosphorus  may  then  be  precipitated  in  the 
filtrate.     In  precipitating  phosphoric  acid  with  magnesia  mixture,  add 
the  reagent  drop  by  drop  and  stir  the  liquid  constantly,  so  that  the 
precipitate  separates  slowly  and  in  a  crystalline  form.     Otherwise  it 
will  be  impure,  containing  magnesia  in  excess  and  molybdic  anhydride. 


DETERMINATION  OF  PHOSPHORUS  37 

The  magnesium  pyrophosphate  must  be  ignited  thoroughly  and  with 
access  of  air  to  drive  off  any  trace  of  MoOs  it  may  contain. 

16.  If  the  sample  to  be  analyzed  contains  vanadium,  the  yellow 
precipitate  will  be  contaminated  with  it,  making  the  precipitate  more 
soluble.     When  vanadium  is  present  the  precipitate  will  have  an  orange 
color  instead  of  being  yellow. 

17.  Since  complete  precipitation  of  the  phosphorus  as  pure  ammonium 
phosphomolybdate  with  constant  composition  is  only  possible  under 
certain  closely  controlled  conditions,  it  is  necessary  for  the  chemist  to 
find  out  for  himself  by  repeated  experiment  exactly  what  these  condi- 
tions are,  and  to  standardize  his  solutions  and  make  his  determinations 
under  exactly  the  same  conditions,  keeping  in  mind  the  many  things 
which  may  cause  error. 

To  determine  the  phosphorus,  the  yellow  precipitate  may  be  dried 
and  weighed  as  such,  or  it  may  be  ignited  to  P2O524MoO3  at  a  tempera- 
ture of  450°C.  for  ten  minutes,  or  the  phosphorus  may  be  determined 
in  the  yellow  precipitate  by  volumetric  methods;  thus  it  may  be  re- 
duced by  nascent  hydrogen  to  Moi20ig,  which  is  then  oxidized  by 
standard  permanganate  back  to  its  original  condition.  Or  the  yellow 
precipitate  which  is  an  acid  anhydride,  may  be  titrated  by  standard 
alkali.  Lastly  the  yellow  precipitate  may  be  dissolved  in  ammonia, 
and  the  phosphorus  precipitated  with  magnesia  mixture  and  weighed 
as  magnesium  pyrophosphate. 

For  properties  of  the  yellow  precipitate  and  the  effects  of  impurities  and 
associated  substances,  see 

HUNDSHAGEN,  Z.  Anal.  Chem.,  XXVIII,  p.  141;  also  Chem.  News, 
Vol.  LX,  p.  169. 

DROWN,  Trans.  Am.  Inst.  Mining  Eng.,  XVIII,  p.  90. 

SHIMER,  Trans.  Am.  Inst.  Mining  Eng.,  XVII,  p.  100. 

HAMILTON,  J.  Soc.  Chem.  Ind.,  X,  p.  904. 

BABBITT,  J.  Anal,  and  App.  Chem.,  VI,  p.  381. 

PATTINSON,  J.  Soc.  Chem.  Ind.,  XIV,  p.  443. 

MAHON,  J.  Am.  Chem.  Soc.,  1898,  p.  429. 

BAXTER,  Am.  Chem.  J.,  XXVIII,  p.  298 
On  the  precipitation  by  magnesia: 

GOOCH,  Am.  Chem.  J.,  I,  p.  391. 

FRANK  and  HINREICHSEN,  Stahl  u.  Eisen,  XXVIII,  p.  295,  "  Effect 
of    Arsenic." 

Note. — According  to  Chesneau,  to  get  a  pure  yellow  precipitate,  the 
first  yellow  precipitate  should  be  dissolved  in  ammonia,  then  acidi- 
fied with  nitric  acid,  then  after  the  precipitate  comes  down,  an  excess 
of  molybdic  acid  solution  is  added,  the  precipitate  allowed  to  settle, 


38  METALLURGICAL  ANALYSIS 

and  then  the  phosphorus  determined  gravimetrically  or  volumetrically. 
See  Rev.  Metal.,  V,  237-69. 

DETERMINATION   OF   PHOSPHORUS   WITH   FINAL   WEIGHING   AS 
MAGNESIUM  PYROPHOSPHATE 

This  method  is  free  from  the  chances  of  error  due  to  the  presence  of 
impurities  in  the  yellow  precipitate.  It  is  gravimetric  and  the  phos- 
phoric acid  is  finally  weighed  in  a  form  not  subject  to  variation  in  com- 
position if  care  is  taken  in  the  precipitation.  It  is  applicable  to  all 
kinds  of  material,  and  to  any  percentage  of  phosphoric  acid;  hence  it  is  a 
standard  method  to  which  final  reference  must  be  made  in  all  important 
determinations. 

Process  for  Iron  Ores. — (In  the  absence  of  more  than  traces  of 
titanium  or  arsenic.)  Weigh  1  to  5  grams,  depending  upon  the 
percentage  of  phosphorus,  of  the  very  finely  pulverized  ore.  Put 
it  into  a  4  in.  porcelain  dish  or  casserole,  add  1  c.c.  nitric  acid, 
then  concentrated  HC1,  using  10  c.c.  for  each  gram  of  ore  taken, 
and  then  add  15  c.c.  more,  cover  with  a  watch-glass,  warm  until 
all  the  iron  appears  to  be  in  solution,  then  boil  down  to  dryness, 
keeping  covered  to  avoid  spattering.  Dry  on  a  hot  plate  until 
the  acid  is  expelled,  then  add  from  30  to  50  c.c.  of  concentrated 
HC1,  cover  and  digest  until  all  the  iron  is  dissolved.  Now  boil 
down  until  the  volume  of  the  liquid  does  not  exceed  10  or  15  c.c. 
If  the  dish  is  kept  covered,  there  need  be  no  formation  of  dry 
salt  on  the  sides.  Add  water  until  the  volume  is  40  or  50  c.c., 
washing  off  the  cover  and  sides  of  the  dish.  Filter  into  a  250  c.c. 
beaker,  using  a  small  filter;  transfer  the  residue  to  a  filter  and 
wash  until  there  is  no  acid  taste  to  the  washings. 

Dry  and  ignite  the  residue.  With  ordinary  ores,  if  light  colored 
and  not  too  large  in  amount,  it  is  generally  practically  free  from 
phosphorus,  and  may  be  thrown  away.  In  case  the  ore  is  an 
unknown  one,  and  occasionally  even  on  known  ones,  the  insol- 
uble residue  should  be  fused  with  sodium  carbonate,  the  fusion 
dissolved  in  HC1,  evaporated  to  dryness,  and  heated  to  dehy- 
drate the  silica.  Dissolve  the  residue  in  2  or  3  c.c.  of  HC1  and 
10  c.c.  of  water  and  filter  into  the  beaker  containing  the  main 
filtrate. 

Instead  of  proceeding  as  above,  the  filtrate  from  a  silica  de- 
termination may  be  used  for  the  determination  of  phosphorus. 


DETERMINATION  OF  PHOSPHORUS  39 

The  filtrate  should  not  much  exceed  100  c.c.  To  it  add  10  c.c. 
of  concentrated  HN03,  and  then  NH4OH  until  a  precipitate  of 
Fe(OH)3  is  formed  which  does  not  disappear  on  stirring.  Now 
add  concentrated  HNO3  until  the  precipitate  just  dissolves,  then 
add  3  to  5  c.c.  more,  which  should  give  to  the  solution  a  clear 
amber  color  without  any  red  tint.  The  solution  will  now  be 
quite  warm.  Heat  if  necessary  to  80°C.  and  add  from  a  pipette 
and  with  vigorous  stirring  50  c.c.  of  molybdic  acid  solution.  Stir 
the  solution  vigorously  for  several  minutes  more.  Vigorous 
stirring  greatly  lessens  the  time  required  for  precipitation.  Allow 
to  stand  until  the  liquid  is  clear  and  the  precipitate  has  all 
settled  (this  should  not  require  more  than  one  hour);  remove  a 
portion  of  the  clear  liquid  with  a  pipette  and  test  it  by  adding 
a  little  more  molybdic  acid  solution  and  warming,  to  make  sure 
that  all  the  phosphoric  acid  is  precipitated. 

Filter  the  liquid  through  a  7-cm.  filter.  Transfer  the  precipi- 
tate to  the  filter  and  wash  free  from  iron,  with  a  1  per  cent,  solu- 
tion of  ammonium  nitrate  very  slightly  acidified  with  HNO3. 
The  washing  must  be  thorough  or  difficulty  will  be  experienced 
when  dissolving  the  precipitate,  as  phosphates  of  iron  and  alu- 
mina may  form  and  clog  up  the  filter.  When  the  precipitate  is 
washed,  put  the  beaker  in  which  the  precipitation  was  made  under 
the  funnel  and  redissolve  the  precipitate  on  the  filter  with  20  to 
30  c.c.  of  dilute  NH4OH  (about  one  part  of  concentrated  am- 
monia to  four  of  water).  When  it  is  dissolved  and  the  liquid 
has  all  run  through,  wash  the  filter  three  or  four  times  with  water, 
then  with  a  little  dilute  HC1,  to  dissolve  any  ferric  or  other  in- 
soluble phosphate  present,  and  finally  with  water.  Use  care  in 
washing,  letting  each  portion  of  water  run  through  before  adding 
another  so  as  to  keep  the  volume  of  the  filtrate  small.  This 
should  not  exceed  100  c.c.  and  is  usually  much  less.  The  filtrate 
should  now  be  clear  and  colorless.  If  it  is  cloudy  or  colored  (due 
to  a  little  iron),  add  HC1  until  the  liquid  is  acid  (the  yellow  pre- 
cipitate usually  separates),  then  add  four  or  five  drops  of  a  satu- 
rated solution  of  citric  acid*  then  NH4OH  to  make  the  liquid 
strongly  alkaline.  This  will  give  a  clear  liquid,  the  citric  acid 
holding  the  iron  in  solution. 

Now  add  drop  by  drop  a  considerable  excess  of  magnesia  mix- 
ture, stirring  the  liquid  constantly.  Estimate  the  amount  from 


40  METALLURGICAL  ANALYSIS 

the  probable  percentage  of  phosphorus  in  the  ore  taken.  Con- 
tinue to  stir  the  solution  vigorously  for  four  or  five  minutes,  then 
add  NH4OH  until  the  solution  smells  strongly  of  ammonia. 
Let  it  stand  until  the  precipitate  of  MgNH4PO4  has  settled  com- 
pletely (one  or  two  hours).  The  precipitate  should  be  white  and 
crystalline;  if  red  or  flaky,  the  results  will  be  inaccurate.  Filter 
on  a  small  filter  or  better  on  a  Gooch  perforated  crucible.  Wash 
with  water  containing  one-tenth  its  volume  of  concentrated 
NH4OH  and  a  little  NH4NO3,  dry,  ignite  and  weigh  as  Mg2P2O7. 
This  contains  0.2787  of  phosphorus. 

It  is  essential  that  the  filtrate  from  the  phosphorus  precipitate 
should  give  at  once  a  strong  reaction  for  magnesium  when  tested 
with  a  drop  of  a  solution  of  sodium  phosphate,  as  a  considerable 
excess  of  reagent  is  necessary  to  completely  precipitate  the 
phosphorus. 

Solutions  Required.  1.  "Magnesia  Mixture." — Dissolve  22 
grams  of  dry  calcined  magnesia  in  as  little  HC1  as  possible. 
When  dissolved,  add  more  of  the  magnesia  until  some  remains 
undissolved,  dilute  with  several  times  its  volume  of  water  and 
boil.  Any  iron  oxide,  alumina  and  phosphoric  acid  will  be  pre- 
cipitated. Filter  the  solution,  add  280  grams  of  NH4C1,  800  c.c. 
of  water  and  200  c.c.  of  NH4OH,  sp.  gr.  0.90.  When  all  dissolved, 
dilute  to  2000  c.c.  Let  stand  a  day  or  two  and  decant  or  filter 
the  solution  from  any  precipitate.  Ten  cubic  centimeters  of  this 
reagent  will  precipitate  about  0.07  gram  of  phosphorus. 

2.  "Molybdic  Acid  Solution."— Add  to  100  grams  of  molybdic 
anhydride  300  c.c.  of  water,  and  then  120  c.c.  of  NH4OH,  sp.  gr. 
0.90.  This  will  dissolve  the  MoO3.  The  solution  must  smell 
distinctly  of  ammonia;  if  it  does  not,  add  more.  Unless  the 
solution  is  clear,  filter  it,  then  dilute  to  about  800  c.c.  Now  mix 
500  c.c.  of  nitric  acid,  sp.  gr.  1.42,  with  enough  water  to  make 
about  1200  c.c.  Cool  both  solutions  and  mix  by  pouring  the 
MoO3  solution  into  the  diluted  nitric  acid  solution,  pouring  slowly 
and  with  stirring.  The  volume  should  now  be  about  2000  c.c. 
Add  to  the  solution  three  or  four  drops  of  a  10  per  cent,  sodium 
phosphate  solution,  shake  thoroughly  and  allow  to  settle  over 
night.  About  once  every  week  or  oftener  another  drop  or  two 
of  the  phosphate  solution  should  be  added  and  the  yellow  pre- 
cipitate formed  allowed  to  settle  over  night.  When  used,  the 


DETERMINATION  OF  PHOSPHORUS  41 

clear  solution  should  be  pipetted  off  or  filtered.  The  reason  for 
adding  the  phosphate  solution  is  as  follows :  The  molybdic  acid 
solution  on  standing  gradually  changes  with  the  separation  of 
Mo03  or  ammonia  tetramolybdate  in  too  fine  a  condition  to 
settle.  The  addition  of  the  phosphate  causes  the  precipitation 
of  ammonium  phosphomolybdate,  which  on  settling  carries  down 
out  of  the  solution  the  separated  molybdic  anhydride,  etc. 

If  the  solution  of  molybdic  acid  in  ammonia  is  not  diluted  suffi- 
ciently, or  if  the  above  directions  are  not  followed  as  to  mixing, 
molybdic  anhydride  may  separate  from  the  solution  as  dense 
curdy  precipitate.  Forty  cubic  centimeters  of  the  solution  will 
precipitate  about  0.04  gram  of  phosphorus.  Pure  Mo03  must  be 
used  in  this  formula.  Some  of  that  on  the  market  is  largely 
ammonium  molybdate. 

MODIFICATION  OF  THE  PROCESS  FOR  ORES  CONTAINING 
TITANIUM 

When  ores  contain  titanium  in  large  amount,  the  residue  will  contain 
considerable  iron  and  phosphorus.  The  'solution  of  the  ore  may 
become  turbid  on  dilution,  and  the  residue  run  through  the  filter  on 
washing. 

Some  of  the  titanium  usually  goes  into  solution  and  may  delay  the 
precipitation  of  phosphorus.  In  such  cases  a  larger  excess  of  molybdic 
acid  solution  should  be  used,  and  a  longer  time  given  for  the  separation 
of  the  precipitate. 

Process  of  Analysis. — Weigh  out  the  ore  and  dissolve  it  in  HC1 
as  in  the  regular  process.  If  the  filtrate  from  the  insoluble  residue 
is  not  clear  add  a  little  HNO3  and  warm,  which  will  probably 
clear  it.  If  a  slight  turbidity  remains  it  is  of  no  importance  and 
may  be  neglected.  Now  proceed  with  the  filtrate  as  in  the  regu- 
lar process.  After  the  yellow  precipitate  has  been  dissolved  in 
ammonia  and  the  filter  washed  as  directed,  dry  and  burn  the 
filter  and  add  the  ash  to  the  insoluble  residue.  This  is  necessary, 
as  insoluble  compounds  of  phosphorus  and  titanium  may  be  re- 
tained in  the  filter.  This  residue  is  now  mixed  with  eight  times 
its  weight  of  dry  Na2CO3  and  fused  as  for  silica.  Boil  the  fusion 
with  water  until  thoroughly  disintegrated.  The  phosphorus 
passes  into  solution  as  phosphate;  while  the  Ti02  remains  insoluble 


42  METALLURGICAL  ANALYSIS 

as  titanate.  Filter  the  liquid  from  the  insoluble  matter,  acidu- 
late the  filtrate  with  HN03  and  evaporate  to  dryness.  Add  a 
little  HN03,  then  water  and  filter  from  the  separated  8162. 

Add  to  the  filtrate  25  c.c.  molybdic  acid  solution  and  warm, 
filter  off  the  yellow  precipitate  and  treat  it  exactly  like  that  from 
the  main  solution.  Add  the  phosphorus  thus  obtained  to  that 
obtained  from  the  first  solution. 

The  foregoing  treatment  is  satisfactory  for  ores  with  moderate 
amounts  of  Ti02.  Where  much  is  present,  direct  fusion  of  the  ore  is 
advisable. 

REFERENCES: 

See  a  valuable  paper  by  DROWN  and  SHIMER,  Trans.  Am.  Inst.  Mining 
Eng.,  X,  p.  137.  Also  PATTINSON,  J.  Soc.  Chem.  Ind.,  1895,  p.  443. 
Discussion,  p.  1022. 

When  ores  contain  arsenic  there  is  always  danger  that  the  final  results 
will  be  high  from  the  presence  of  magnesium  arsenate. 

In  this  case  proceed  as  follows :  To  the  filtrate  from  the  insol- 
uble residue,  which  should  be  in  a  small  Erlenmeyer  flask,  add 
a  solution  of  Na2C03  until  the  liquid  becomes  dark  colored,  then 
add  gradually,  a  solution  of  pure  crystallized  sodium  sulfite 
(Na2SO3)  prepared  by  dissolving  the  salt  in  water  1  to  5,  and  add- 
ing HC1  until  the  solution  reacts  slightly  acid.  Heat  the  iron 
solution  to  boiling,  shaking  occasionally.  If  any  precipitate 
forms,  redissolve  it  with  a  few  drops  of  HC1.  By  this  time  the 
solution  should  be  colorless  and  all  the  iron  reduced  to  the  ferrous 
state;  if  not,  continue  the  warming.  When  reduced  add  10  c.c. 
HC1,  and  boil  until  the  odor  of  SO2  has  gone  (usually  about  three 
minutes).  Remove  from  the  flame  and  pass  a  stream  of  H2S  gas 
through  the  liquid  for  15  or  20  minutes,  or  until  all  the  As2S3  is 
precipitated.  (The  volume  of  the  liquid  should  not  exceed  150 
c.c.)  The  arsenic  and  any  copper  present  separate  completely 
as  sulfides.  Filter  the  solution  rapidly  into  a  beaker  and  wash 
with  a  little  H2S  water.  Now  boil  the  filtrate  until  all  the  odor  of 
H2S  has  disappeared,  then  add  HNO3  drop  by  drop  to  the  hot 
liquid  until  the  change  of  color  shows  that  the  iron  is  changed  to 
the  ferric  state.  The  liquid  should  become  perfectly  clear.  A 
faint  cloud  of  separated  sulfur  may  form,  but  will  disappear  on 
heating  and  does  not  harm.  From  this  point  proceed  exactly 


DETERMINATION  OF  PHOSPHORUS  43 

as  with  the  filtrate  from  the  insoluble  residue  in  ores  when  arsenic 
is  not  present. 

The  process  depends  upon  the  complete  precipitation  of  arsenic 
by  H2S  in  hot  strongly  acid  solutions.  The  reduction  of  the  iron  is 
necessary  to  prevent  a  large  separation  of  sulfur  from  the  action  of  the 
H2S  on  the  FeCl3. 

The  As2Sa  precipitate  may  be  used  for  the  determination  of  arsenic, 
provided  the  solution  has  not  been  boiled  before  precipitation  by  H2S, 
which  would  cause  volatilization  of  AsCl3.  See  Fresenius  Quantitative 
Analysis  for  details. 

DETERMINATION  OF  PHOSPHORUS  IN  BLACK  BAND  AND  OTHER 
ORES  WHICH  CONTAIN  MUCH  CARBONACEOUS  MATTER 

These  should  be  weighed  out  in  a  porcelain  crucible  and  ignited, 
taking  care  not  to  heat  so  rapidly  as  to  cause  loss  by  blowing  out 
of  fine  particles.  Set  the  crucible  on  its  side  over  a  small  flame 
and  let  the  material  gradually  burn  away  until  all  carbon  is  gone, 
and  an  "  ash  "  is  left.  Treat  this  by  the  regular  process.  Avoid 
a  high  temperature  in  burning  or  the  material  will  cake,  thus  de- 
laying the  combustion  and  leading  to  imperfect  solution.  A 
dull  red  heat  is  sufficient. 


DETERMINATION  OF  PHOSPHORUS  IN  MILL  CINDER 

Two  points  here  need  attention.  First,  the  material. being  a  soluble 
silicate,  it  should  be  decomposed  by  weak  acid  and  evaporated  to  dry- 
ness  as  in  the  determination  of  silica  after  fusion.  Second,  all  mill 
cinder  contains  particles  of  metallic  iron,  in  which  phosphorus  is  present 
as  phosphide.  These  would  evolve  PH3  gas  when  dissolved  in  HC1,  so 
HN03  must  be  used  to  oxidize  this  phosphorus. 

Proceed  as  follows:  Weigh  1  gram  into  a  porcelain  dish,  add 
20  c.c.  HN03,  1.2  sp.  gr.,  stir  well  to  prevent  caking  and  warm 
till  action  ceases,  then  add  10  c.c.  H2O  and  10  c.c.  concentrated 
HC1.  Evaporate  to  dry  ness  and  heat  on  an  iron  plate  to  200°C. 
for  half  an  hour.  Add  10  c.c.  HC1,  and  digest  until  all  the  iron 
is  dissolved.  Dilute,  filter,  and  proceed  as  with  an  ore. 


44  METALLURGICAL  ANALYSIS 

DETERMINATION  OF  PHOSPHORUS  BY  THE  MOLYBDATE-MAGNESIA 

PROCESS 

The  phosphorus  in  iron  and  steel  exists  principally  as  phosphide. 
When  these  metals  are  treated  with  ordinary  oxidizing  solvents,  such  as 
dilute  HN03,  or  KC103  +  HC1,  the  oxidation  of  the  phosphorus  is  in- 
complete. Even  concentrated  HN03  fails  to  convert  all  the  phosphorus 
into  tribasic  phosphoric  acid.  The  metal  must  not  be  dissolved  in  HC1 
or  H2S04  as  they  would  cause  phosphorus  to  pass  off  as  phosphine  gas 
(PH3). 

These  metals  also  contain  carbon  compounds  which  pass  into  solution 
in  HN03,  forming  a  dark  colored  substance,  and  the  presence  of  this 
dissolved  carbonaceous  matter  is  generally  supposed  to  interfere  with 
the  precipitation  of  the  yellow  precipitate.  It  seems  probable,  however, 
from  certain  experiments  that,  if  the  phosphoric  acid  is  in  the  tribasic 
state,  this  organic  matter  is  without  influence.  It  is  certain,  however, 
that  unless  the  oxidizing  action  is  strong  enough  to  destroy  this  carbon- 
aceous matter  completely,  the  phosphorus  is  not  all  oxidized  and  hence 
not  precipitated  completely. 

The  oldest  and  most  certain  method  of  oxidation  is  the  "dry  oxidation 
method."  It  consists  in  dissolving  the  metal  in  HN03  either  concen- 
trated or  dilute,  sp.gr.  1.2,  and  then  evaporating  the  solution  to  dry- 
ness.  The  dry  mass  of  basic  ferric  nitrate  is  then  heated  to  about 
200°C.  for  some  time.  At  this  temperature  the  salts  are  decomposed, 
the  iron  largely  converted  to  ferric  oxide,  and  the  dissolved  carbon  and 
the  phosphorus  completely  oxidized.  This  residue  can  then  be  dissolved 
in  HC1  and  treated  like  an  ore.  The  method  is  always  reliable  and  in- 
volves no  delicate  adjustments. 

To  save  the  time  required  for  evaporating  the  solution  and  baking 
the  residue,  several  methods  have  been  devised  for  oxidizing  the  material 
in  the  nitric  acid  solution.  The  reagents  most  successfully  used  are 
potassium  permanganate,  chromic  acid  and  ammonium  persulfate. 
Aqua  regia,  potassium  chlorate  or  chlorine  fail  to  oxidize  the  material 
completely. 

When  permanganate  is  used  there  is  a  separation  of  Mn02  as  a  brown 
precipitate  which  holds  phosphorus  and  must  be  entirely  redissolved 
before  filtering  from  the  residue  or  precipitating  the  phosphorus. 
This  is  accomplished  by  adding  a  reducing  agent,  such  as  oxalic  acid, 
ferrous  sulfate,  sugar,  or  potassium  nitrite,  to  the  acid  liquid.  Any 
considerable  excess  should  be  avoided.  The  MnC>2  is  reduced  to  MnO 
and  dissolved  in  the  acid. 

Wet  methods  are  more  rapid  but  are  not  adapted  to  all  kinds  of  mate- 


DETERMINATION  OF  PHOSPHORUS  45 

rial  and  must  only  be  used  where  they  have  been  shown  to  apply  by 
repeating  checking  of  the  results  with  the  standard  methods. 

When  pig-iron  or  steel,  containing  silicon,  is  dissolved  in  HN03, 
evaporated  and  "baked,"  the  HC1  solution  of  the  residue  will  be  found 
to  filter  very  slowly  because  silicic  acid  in  HN03  solution  is  not  fully 
dehydrated  on  evaporation  even  if  the  residue  is  heated  to  200°C. 
Hence  when  the  residue  is  treated  with  HC1  some  of  the  Si02  goes  into 
the  solution  and  leaves  the  rest  in  a  highly  gelatinous  form. 

The  SiC>2  left  after  the  evaporation  of  an  HC1  solution  is  much  more 
granular  and  easily  filtered  off.  Therefore,  in  all  cases  where  silicon  is 
present  to  any  extent  the  HC1  solution  of  the  "baked"  residue  should 
be  evaporated  to  hard  dryness  and  again  taken  up  in  HC1.  This  sec- 
ond evaporation  takes  but  little  time  and  is  essential,  especially  with 
cast-iron,  if  a  long  and  tedious  filtration  is  to  be  avoided. 

It  is  stated  that  the  addition  of  a  few  drops  of  HF  or  a  little  NH4F 
to  the  first  HC1  solution  will  cause  it  to  filter  more  rapidly  and  often 
render  the  second  evaporation  unnecessary. 

Process  for  Phosphorus  in  Iron  and  Steel. — Take  from  1  to  5 
grams  of  the  well-mixed  borings.  Treat  them  in  a  covered  cas- 
serole or  dish  with  25  to  75  c.c.  of  HNO3,  sp.  gr.  1.2  (made  by 
mixing  water  and  concentrated  HN03  in  equal  volumes).  Add 
the  acid  cautiously  to  prevent  boiling  over.  Heat  until  action 
has  ceased  and  boil  down  to  dryness,  using  care  to  prevent  spat- 
tering, and  keeping  the  dish  covered.  When  dry,  set  on  a  hot 
iron  plate  and  heat  the  dish  to  about  200°C.  for  from  30  minutes 
to  one  hour;  at  the  end  of  this  time  the  material  should  be  hard 
and  scaly  and  show  no  trace  of  acid  fumes.  Now  add  from  15  to 
25  c.c.  concentrated  HC1,  and  digest  until  the  iron  is  dissolved. 
Again  evaporate  to  hard  dryness  and  dissolve  a  second  time  in 
concentrated  HC1,  then  proceed  as  with  an  iron  ore. 

Many  steels  will  leave  no  residue  insoluble  in  HC1.  In  this 
case  nitration  as  well  as  the  second  evaporation  is  unnecessary. 

The  phosphorus  retained  in  the  residue  practically  amounts  to 
nothing  in  the  case  of  irons  and  steels. 

To  make  the  filtration  easy,  add  to  the  above  HC1  solution 
about  50  c.c.  water  and  boil  for  about  5  minutes.  Then  let  it 
settle  completely,  decant  off  the  clear  liquid  through  the  filter, 
and  transfer  and  wash  the  residue  with  warm  water,  adding  a 
little  HC1  at  first.  This  treatment  seems  to  cause  a  consolida- 
tion of  the  SiO2. 


46  METALLURGICAL  ANALYSIS 

PROCESS  FOR  FERROSILICON  AND  OTHER  DIFFICULTLY  SOLUBLE 

ALLOYS 

Ferrosilicon  with  over  10  per  cent,  of  silicon  is  only  slightly  attacked 
by  HN03  or  aqua  regia.  This  and  other  insoluble  alloys  cannot  be 
treated  by  the  foregoing  method  for  the  determination  of  phosphorus. 
With  ferrosilicon,  if  the  percentage  of  silicon  is  not  too  high,  the  addition 
of  a  little  HF  or  NaF  to  the  HN03  and  metal  in  the  dish  will  cause  it  to 
dissolve  and  then  the  regular  method  can  be  followed.  About  as  much 
NaF  should  be  added  as  there  is  silicon  present.  The  metal  should  be 
very  finely  pulverized;  this  presents  no  difficulty  as  these  alloys  are  all 
brittle.  The  metal  should  be  crushed  in  a  steel  mortar  until  it  will  all 
go  through  a  100-mesh  sieve  and  then  the  portion  to  be  used  in  the 
analysis  rubbed  down  in  an  agate  mortar. 

Samples  not  attacked  by  the  fluoride  must  be  fused.  Mix  the 
very  finely  ground  sample  with  five  or  six  times  its  weight  of  a 
fusion  mixture  of  equal  parts  of  Na2C03  and  NaNO3  and  fuse  in  a 
platinum  crucible.  Apply  the  heat  cautiously  until  the  first  reac- 
tion is  over  and  the  mass  is  quiet,  then  raise  the  temperature  till 
fusion  is  complete.  Avoid  using  a  higher  temperature  than  is 
necessary  as  the  platinum  is  likely  to  be  attacked.  The  fusion 
can  then  be  taken  up  in  water  and  HC1  and  the  phosphorus  de- 
termined as  usual. 

HC1  must  not  be  added  in  the  crucible  as  chlorine  may  be 
formed  and  attack  it,  but  after  the  mass  has  been  soaked  out 
with  water  any  adhering  Fe203  may  be  dissolved  in  a  little  HC1. 

Instead  of  dissolving  the  whole  fusion  in  HC1,  it  may  be  boiled 
with  water,  the  lumps  being  crushed  fine,  and  the  solution  then 
filtered  from  the  Fe2O3  and  acidified;  the  filtrate  will  contain  all 
the  phosphorus  as  sodium  phosphate  with  some  silicate.  The 
residue  should  be  tested,  however,  in  important  cases.  A  blank 
must  be  run  on  the  reagents. 

Sodium  peroxide  is  sometimes  used  instead  of  the  nitrate;  it  works 
rapidly  and  is  a  powerful  oxidizing  agent,  but  is  not  so  easy  to  obtain 
pure.  It  acts  at  so  low  a  temperature  that  nickel  crucibles  can  be  used 
in  the  fusions  and  the  wear  on  the  platinum  saved.  These  fusions  are 
very  destructive  to  platinum,  which  should  not  be  used  when  the  metal 
is  fused  with  sodium  peroxide  alone. 

In  fusing  ferrosilicon  with  sodium  peroxide  alone  a  large  excess  of  the 


DETERMINATION  OF  PHOSPHORUS  47 

reagent  must  be  used  or  the  reaction  becomes  very  violent;  at  least 
eight  parts  of  peroxide  to  one  of  metal  are  required.  The  temperature 
of  fusion  need  not  exceed  a  dull  red. 


DETERMINATION  OF  PHOSPHORUS  BY  WEIGHING  THE  YELLOW 

PRECIPITATE 

This  method  is  generally  used  as  a  "rapid  method."  It  is  not, 
however,  as  rapid  as  the  volumetric  method  for  phosphorus,  but  it  is 
the  most  rapid  of  the  gravimetric  methods. 

Since  accurate  results  by  this  method  depend  upon  purity  of  the 
yellow  precipitate,  and  uniform  composition  of  the  same,  it  is  necessary 
that  the  conditions  of  precipitation  be  strictly  controlled  and  that  the 
process  be  checked  by  running  the  phosphorus  in  a  standard  sample 
under  exactly  the  same  conditions  as  obtain  in  the  routine  work  of 
the  laboratory. 

The  yellow  precipitate  is  quite  hygroscopic,  hence  it  must  be  weighed 
promptly  and  with  the  least  possible  exposure  to  the  air. 

As  the  yellow  precipitate  has  1.63  per  cent,  of  phosphorus  it  is  con- 
venient to  take  that  amount  in  grams  for  analysis.  The  drying  and 
weighing  of  more  than  0.4  gram  of  yellow  precipitate  is  difficult,  hence 
for  ores  having  over  0.4  per  cent,  of  phosphorus,  take  one-half  of  the 
above  amount  (0.815). 

Process  for  Iron  Ores. — Weigh  1.63  grams  of  the  finely  pul- 
verized ore  into  a  4-in.  casserole,  add  25  c.c.  concentrated  HC1, 
digest,  evaporate  to  dryness  and  heat  as  in  the  former  process. 
Now  add  20  c.c.  HC1,  and  digest  until  all  the  iron  is  dissolved. 
Add  30  c.c.  of  water,  boil,  let  settle  and  filter  into  a  beaker  of 
250  c.c.  capacity;  wash  with  small  portions  of  water  several  times. 
The  volume  of  the  nitrate  need  not  exceed  70  or  80  c.c.  Now  add 
35  c.c.  of  strong  nitric  acid  and  boil  down  rapidly  until  the  volume 
of  the  liquid  is  15  c.c.  Take  from  the  hot  plate,  wash  off  the 
cover  and  dilute  to  50  c.c.  Add  NH4OH  until  a  permanent  pre- 
cipitate forms,  then  add  nitric  acid  until  the  precipitate  just  dis- 
solves, then  3  c.c.  more.  Heat  to  80°C.,  add  50  c.c.  of  molybdic 
acid  solution  slowly  and  with  stirring  and  continue  the  stirring 
for  several  minutes.  The  precipitate  should  settle  out  perfectly 
clear  in  one-half  hour. 

Fold  a  4-cm.  filter,  put  in  the  air-bath  and  dry  at  110°C.  for 
15  minutes.  Place  it  quickly  between  two  watch-glasses  which 


48  METALLURGICAL  ANALYSIS 

fit  tightly,  and  weigh  immediately.  The  weights  for  the  watch- 
glasses  should  already  be  on  the  balance  pan  before  the  paper  is 
weighed.  Weigh  to  the  nearest  milligram. 

Place  the  paper  in  a  small  funnel,  filter  and  transfer  the  precipi- 
tate to  it.  Wash  out  the  beaker  and  wash  the  precipitate  five 
times  with  a  solution  of  molybdic  acid  (1  part  molybdic  acid  solu- 
tion to  3  parts  water).  Finally  wash  the  precipitate  at  least  six 
times  with  2  per  cent.  HN03  solution.  Set  the  funnel  and  con- 
tents in  an  air-bath  and  dry  at  110°  for  30  minutes  after  all  visible 
moisture  has  disappeared.  Quickly  place  the  paper  between  the 
watch-glasses  and  weigh.  The  difference  in  weight  between  the 
first  and  second  weighings  gives  the  yellow  precipitate  and  this 
in  grams  gives  the  percentage  of  phosphorus. 

Instead  of  weighing  the  yellow  precipitate  as  such,  the  follow- 
ing process  may  be  used :  Place  the  funnel  with  the  precipitate  in 
it  above  a  weighed  platinum  crucible  and  wash  the  precipitate 
with  hot  NH4OH  until  it  is  entirely  in  the  crucible.  Evaporate 
the  solution  in  the  crucible  to  dryness,  then  heat  to  400-^50°C. 
in  an  air-bath.  Do  not  heat  to  a  red  heat  as  some  Mo03  will 
volatilize.  Ten  minutes'  heating  is  enough.  The  factor  for 
phosphorus  in  the  P2O524MoO3  thus  obtained  is  0.0169;  that  is, 
the  residue  contains  1.69  per  cent,  phosphorus. 

Process  for  Iron  and  Steel. — Weigh  1.63  grams  of  the  well- 
mixed  borings  into  a  4-in.  casserole.  Add  cautiously  35  c.c. 
HNO3,  sp.  gr.  1.2,  boil  to  dryness,  then  bake  for  30  minutes  on  a 
hot  plate  at  200°C.  Dissolve  in  20  c.c.  HC1  and  if  silicon  is 
present  again  evaporate  to  dryness  and  dissolve  a  second  time. 
Now  proceed  as  in  the  case  of  ores,  except  that  if  the  steel  dis- 
solves without  residue  filtration  is  unnecessary. 

The  above  methods  assume  that  the  phosphorus  all  passes  into 
solution  and  that  arsenic  is  absent.  Titaniferous  and  arsenical 
ores  and  metals  must  be  treated  by  the  first  method. 

The  yellow  precipitate  method  as  described,  may  be  much 
shortened  for  steel  and  pig-iron  by  using  wet  methods  of  oxida- 
tion. For  the  use  of  permanganate  for  oxidizing  the  phosphorus, 
see  Volumetric  Method  for  Phosphorus  on  page  49. 

The  Chromic  Acid  Method  is  as  follows:  Dissolve  1.63  grams 
of  steel  in  30  c.c.  of  nitric  acid,  sp.  gr.  1.20,  in  a  175  c.c.  Erlen- 
meyer  flask.  Place  the  flask  over  a  burner  and  evaporate  to 


DETERMINATION  OF  PHOSPHORUS  49 

15  c.c.  Add  to  the  boiling  solution  20  c.c.  of  a  solution  of  30 
grams  of  Cr03  in  2000  c.c.  of  HN03,  sp.  gr.  1.42.  Dissolve  the 
chromic  acid  by  heating.  The  solution  will  keep  only  about  two 
weeks. 

Evaporate  the  contents  of  the  flask  to  18  c.c.  Wash  down  with 
7  c.c.  of  water,  cool  to  45°C.,  and  add  60  c.c.  of  clear  molybdic 
acid  solution  previously  heated  to  about  40°C.  Shake  well  for 
five  minutes,  let  settle  for  15  minutes,  filter,  wash  and  weigh. 

VOLUMETRIC  METHODS  FOR  PHOSPHORUS 

These  are  based  on  the  precipitation  of  the  phosphorus  as  phospho^ 
molybdate  and  determination  of  the  amount  of  the  precipitate  by 
estimating  the  molybdic  acid  contained  in  it  volumetrically,  either  by 
reduction  with  zinc  and  titration  with  potassium  permanganate,  or  by 
neutralizing  it  with  standard  alkali. 

Emmerton's  Method.  Titration  by  Permanganate. — When  the 
yellow  precipitate  is  dissolved  in  NH4OH  and  mixed  with  a  very  con- 
siderable excess  of  H2S04,  it  all  remains  in  solution.  If  this  solution  is 
warmed  with  metallic  zinc,  zinc  dissolves,  and  the  molybdic  acid  is 
rapidly  reduced,  giving  first  a  dark  red  and  finally  a  green  solution 
containing,  if  the  reduction  is  complete,  Mo203.  If  this  solution  is 
rapidly  filtered  from  any  undissolved  zinc,  it  can  be  titrated  with  a 
solution  of  potassium  permanganate  which  promptly  oxidizes  the  Mo«03 
back  to  MoOa.  The  solution  becomes  colorless  and  finally  when  oxi- 
dation is  complete  is  colored  pink  by  the  least  excess  of  permanganate. 

The  color  of  the  reduced  solution  depends  somewhat  upon  the  excess 
of  sulfuric  acid  present.  If  this  is  too  large  the  green  color  will  not  be 
reached  and  the  end  of  the  reduction  cannot  be  determined.  The 
smaller  the  excess  of  H2S04  the  sharper  is  the  change  from  red  to  green 
at  the  end. 

Complete  reduction  is  a  matter  of  considerable  difficulty  and  the 
methods  in  use  do  not  always  attain  it.  This  has  given  rise  to  the 
assigning  of  various  formulas  to  the  reduced  product.  Emmerton 
gives  Moi20i9,  which  probably  most  nearly  represents  the  usual  product 
of  the  reduction  method  he  describes.  The  reductor  gives  ratios 
between  the  molybdenum  and  the  oxygen  which  vary  with  the  methods 
of  using  it.  Blair  and  Whitfield  give  for  the  reductor  product  Mo24087. 

REFERENCES: 

EMMERTON,  Trans.  Am.  Inst.  Mining  Eng.,  XV,  p.  93. 
DUDLEY  and  PEASE,  J.  Am.  Chem.  Soc.,  1894,  p.  224. 


50  METALLURGICAL  ANALYSIS 

W.  A.  NOTES,  J.  Am.  Chem.  Soc.,  1894,  p.  553. 
W.  A.  NOYES,  J.  Am.  Chem.  Soc.,  1895,  p.  129. 
BLAIR  and  WHITFIELD,  J.  Am.  Chem.  Soc.,  1895,  p.  747. 
AUCHY,  J.  Am.  Chem.  Soc.,  1896,  p.  955. 

This  uncertainty  as  to  the  reduction  product  makes  the  standard 
permanganate  solution  of  uncertain  value  in  phosphorus  if  standardized 
against  metallic  iron  only;  hence,  it  is  better  to  check  it  against  a  stand- 
ard steel,  ore  or  pig-iron,  of  known  phosphorus  content  which  should 
be  treated  exactly  by  the  method  used  in  the  regular  analysis. 

The  widely  extended  use  of  this  method  shows,  however,  that  although 
there  is  some  uncertainty  as  to  the  nature  of  the  oxide  produced  by 
reduction,  this  possibly  being  different  for  different  workers,  by  working 
always  in  exactly  the  same  way,  the  reduction  is  uniform,  and  hence  the 
titration  is  a  reliable  method  for  estimating  the  yellow  precipitate, 
and  indirectly  the  amount  of  phosphorus. 

Preparation  of  the  Solution  of  Potassium  Permanganate. — To 
compute  the  strength  of  this  solution  assume  that  the  reduction 
of  the  yellow  precipitate  gives  Moi20i9.  Then  the  permanganate 
solution  must  furnish  17  atoms  of  oxygen  for  each  12  molecules 
of  MoOa  present  before  reduction  to  oxidize  the  Moi2Oig  back  to 
MoO3.  The  yellow  precipitate  contains  24  MoOs  to  1  of  P2O5  or 
12  of  MoO3  to  1  of  P;  hence  the  permanganate  must  furnish  17 
atoms  of  oxygen  for  every  atom  of  phosphorus  present  in  the 
precipitate. 

The  permanganate  used  may  be  either  the  one  used  for  titrat- 
ing iron  or  one  made  especially  for  phosphorus  determinations. 
In  the  former  case,  the  value  of  the  permanganate  in  terms  of 
phosphorus  is  obtained  as  follows:  One  atom  of  oxygen  can 
oxidize  two  atoms  of  ferrous  iron  to  ferric  iron;  hence  the  reducing 
power  of  the  reduced  yellow  precipitate  is  equal  to  17X2  or 
34  atoms  of  ferrous  iron.  Therefore, 

One  atom  of  P.  :  34  atoms  of  Fe  : :  X  :  Fe  value  of  the  perman- 
ganate, or  31  : 1898.9  : :  X  :  Fe  value  of  the  permanganate.  Solving 
for  X  we  find  that  the  iron  value  of  the  permanganate  multiplied 
by  0.01634  equals  the  phosphorus  value  of  the  permanganate. 

To  make  a  solution  of  such  strength  that  1  c.c.  equals  0.01  per 
cent,  of  phosphorus  on  a  1  gram  sample,  note  that  two  molecules 
of  permanganate  will  yield  oxygen  thus:  2KMn04+3H2S04  = 
K2SO4-h2MnSO4+3H2O-}-50.  That  is,  two  molecules  of  per- 


DETERMINATION  OF  PHOSPHORUS  51 

manganate  will  give  up  five  atoms  of  oxygen.  'Therefore  to 
yield  17  atoms  of  oxygen  which  is  the  amount  required  to  oxidize 
one  molecule  of  the  reduced  yellow  precipitate  (equivalent  to  one 
atom  of  phosphorus)  requires  17 X%  or  6^  molecules  of  KMn04. 
Therefore : 

6%KMnO4 :  IP.  : :  X  : 0.0001, 

or  1074.6  : 31. 04  :  :X  : 0.0001.  X  equals  0.003462  gram  KMnO4 
per  c.c.  or  3.462  gram  per  liter. 

To  make  the  solution,  heat  1  liter  of  water  to  boiling  and  add 
dilute  KMnO4  until  a  faint  pink  appears.  Cool  to  room  tempera- 
ture and  dissolve  3.462  grams  of  pure  permanganate  in  500  c.c., 
then  dilute  to  a  liter. 

To  standardize,  dissolve  0.8589  gram  (NH4)2S04.FeS04.6H20. 
in  200  c.c.  of  water  and  5  c.c.  H2SO4  and  titrate  to  a  faint  pink. 
This  amount  of  iron  salt  contains  0.1224  gram  of  iron,  which  is 
equivalent  to  0.1224X0.01634  =  0.002  gram  of  phosphorus; 
therefore  20  c.c.  of  the  solution  should  be  required.  If  more  or 
less  is  taken,  calculate  the  amount  of  phosphorus  to  which  1  c.c. 
is  equivalent  by  the  proportion,  n:20  =  0.000l:x,  n  being  the 
amount  used  and  x  the  value  sought. 

The  determination  of  the  value  against  a  known  steel  is  desir- 
able, as  it  gives  a  result  which  is  independent  of  all  assumptions 
as  to  the  nature  of  the  oxide  produced  by  the  zinc  reduction. 
The  permanganate  solution  should  be  kept  in  a  dark  bottle  care- 
fully protected  from  dust  and  other  organic  matter,  and  used  only 
in  burettes  with  glass  stop-cocks. 

Process  for  Iron  or  Steel. — Weigh  3  grams  of  steel  or  1  to  3 
grams  of  iron,  according  to  the  percentage  of  phosphorus,  into 
a  4-in.  casserole,  and  add  25  to  75  c.c.  of  HNO3,  sp.  gr.  1.2.  Add 
the  acid  cautiously  to  avoid  boiling  over.  After  action  has  ceased, 
cover  and  boil  down  to  dryness,  then  bake  on  a  hot  plate  30 
minutes  and  add  20  to  40  c.c.  concentrated  HC1.  Heat  until 
all  the  iron  oxide  is  dissolved. 

If  the  metal  contains  much  more  than  a  trace  of  silicon,  evapo- 
rate the  solution  to  dryness  and  dissolve  again  in  the  same  amount 
of  HC1.  Finally,  boil  down  to  15  c.c.,  being  careful  to  avoid  the 
formation  of  any  dry  crusts  on  the  sides  of  the  dish.  This  is 
accomplished  by  keeping  the  dish  well  covered  and  shaking  it 
around  a  little. 


52  METALLURGICAL  ANALYSIS 

Now  add  20  to  40  c.c.  concentrated  HNO3,  using  the  acid  to 
wash  the  cover.  Boil  down  again  to  10  or  15  c.c.  It  is  essential 
that  no  dry  iron  salt  form  on  the*  sides.  This  is  easily  avoided  by 
covering  with  an  inverted  watch-glass  a  little  smaller  than  the 
dish,  so  that  the  condensed  acid  will  flow  down  the  sides  and  keep 
them  clean.  Cool  slightly,  moving  the  liquid  around  so  as  to 
dissolve  any  crusts  of  ferric  nitrate  formed.  Now  add  30  to  50 
c.c.  of  water  and  filter  into  a  400  c.c.  Erlenmeyer  flask.  The 
volume  should  be  about  75  c.c.  Steels  do  not  require  filtration, 
as  a  rule,  for  they  leave  no  residue  if  low  in  silicon. 

Now  add  NH4OH  until  the  ferric  hydroxide  separates  and 
the  mass  becomes  thick  and  smells  of  ammonia.  Then  add 
strong  HNO3  gradually  until  the  precipitate  redissolves  and  the 
liquid  has  a  clear,  amber  color,  not  the  least  red.  The  volume 
should  now  be  about  150  c.c.;  if  not,  dilute  to  that  amount. 
Then  put  a  thermometer  in  the  liquid  and  bring  the  temperature 
to  80°C.  Now  add  at  once  40  c.c.  of  molybdic  acid  solution. 
Close  the  flask  with  a  rubber  stopper,  wrap  it  in  a  thick  cloth 
and  shake  violently  for  five  minutes. 

This  violent  agitation,  combined  with  the  high  temperature, 
causes  the  yellow  precipitate  to  separate  promptly  and  in  a  par- 
ticularly dense  and  easily  filtered  form. 

Finally,  let  settle  for  a  few  moments,  and  filter  off  the  solution, 
using  a  9-cm.  filter.  Wash  the  flask  and  precipitate  several 
times  with  a  solution  made  by  diluting  the  molybdic  acid  solu- 
tion with  five  times  its  volume  of  water.  Finally,  wash  well 
both  flask  and  precipitate  with  pure  water  until  the  washings 
do  not  react  acid.  Now  set  the  funnel  in  the  flask  and  dissolve 
the  precipitate  back  into  it  with  dilute  NH4OH  (1:4)  using 
altogether  30  c.c.  To  save  time  some  chemists  puncture  the 
filter  and  wash  the  precipitate  through  with  water.  Wash  the 
filter,  using  as  little  water  as  possible. 

Finally  wash  the  filter  again  with  NH4OH  then  with  water. 
Now  add  80  c.c.  of  dilute  H2SO4  (one  volume  to  four  of  water) 
to  the  filtrate  and  then  10  grams  of  pulverized  zinc. 

The  zinc  should  be  fine  enough  to  pass  a  20-mesh  sieve  and 
must  be  as  free  as  possible  from  iron.  The  very  pure  zinc  now 
furnished  for  this  process  will  sometimes  act  very  slowly.  To 
make  it  act  promptly  it  should  first  be  platinized  as  follows: 


DETERMINATION  OF  PHOSPHORUS  53 

Treat  a  quantity  of  the  zinc  with  water,  slightly  acidulated  with 
H2SO4  and  containing  a  few  drops  of  a  solution  of  PtCl4.  After 
the  reaction  has  proceeded  a  few  minutes,  pour  off  the  liquid  and 
wash  the  zinc  thoroughly  with  water;  dry  it  and  preserve  it  in 
a  glass-stoppered  bottle.  The  almost  infinitesimal  trace  of 
platinum  precipitated  on  the  zinc  by  this  treatment  causes  the 
reaction  to  be  rapid  and  powerfully  reducing  on  the  MoO3. 

Now  warm  till  rapid  effervescence  ensues  and  heat  gently 
10  minutes.  At  the  end  of  this  time  reduction  will  be  complete. 
Meanwhile,  fold  a  12-cm.  filter  in  "ribs,"  put  it  in  a  funnel,  and 
as  soon  as  the  reduction  of  the  MoO3  is  complete  pour  the  liquid 
off  from  the  residue  of  the  zinc  into  the  filter,  collecting  the 
filtrate  in  a  white  dish.  Rinse  the  flask  and  zinc  once  with  water 
and  pour  this  on  the  filter  after  the  solution  has  run  through. 
Then  fill  the  filter  with  water  and  let  it  run  through.  Thin 
filter  paper  must  be  used  so  that  the  whole  operation  of  filtration 
and  washing  the  zinc  shall  occupy  but  three  or  four  minutes. 

Instead  of  filter  paper  absorbent  cotton  may  be  used,  a  small 
plug  being  placed  loosely  in  the  neck  of  the  funnel.  This  should 
be  moistened  and  the  solution  poured  directly  on  to  it.  This 
will  filter  very  rapidly  and  satisfactorily. 

Now  run  the  permanganate  into  the  dark  colored  filtrate  till 
the  color  is  discharged,  and  the  last  drop  gives  a  faint  pink  tint, 
marking  the  end  of  the  reaction. 

There  is  always  some  impurity  in  the  zinc,  hence  it  is  essential 
to  make  a  blank  test,  using  the  30  c.c.  of  NH4OH,  the  10  grams 
of  zinc  and  80  c.c.  of  sulfuric  acid  as  before,  but  omitting  the 
yellow  precipitate.  The  filtrate  in  this  test  will  always  consume 
a  small  amount  of  permanganate,  which  must  be  determined, 
and  deducted  from  the  amount  taken  in  the  regular  determina- 
tion, the  difference  being  the  permanganate  solution  equivalent 
to  the  yellow  precipitate. 

The  number  of  cubic  centimeters  of  permanganate  solution 
used,  after  correction  for  error  of  standard,  divided  by  the  num- 
ber of  grams  of  metal  taken  will  give  the  amount  of  phosphorus 
in  hundredths  of  1  per  cent. 

In  working  this  process  it  is  important  to  check  it  from  time 
to  time  upon  material  similar  to  that  to  be  analyzed,  and  in 
which  the  phosphorus  has  been  determined  gravimetrically. 


54  METALLURGICAL  ANALYSIS 

THE  EMMERTON  METHOD  WITH  WET  OXIDATION 

By  substituting  wet  methods  of  oxidation  for  the  baking  in  the  regular 
process  and  using  the  reductor  for  reducing  the  molybdic  acid,  the 
Emmerton  method  becomes  extremely  rapid.  It  then  depends  upon 
such  nice  adjustment  of  conditions,  however,  that  it  should  be  especially 
tested  for  any  variation  in  the  material  treated.  The  permanganate  in 
these  processes  should  be  standardized  against  a  steel  of  approximately 
the  same  phosphorus  content  as  that  to  be  analyzed.  This  is  desirable 
not  only  on  account  of  the  uncertainty  in  the  reduction  product  but 
also  on  account  of  the  fact  that  the  completeness  of  precipitation  of  the 
phosphorus  by  the  molybdic  acid  solution  depends  somewhat  on  the 
treatment  and  also  upon  the  percentage  of  phosphorus  in  the  steel. 
For  example,  if  a  steel  containing  only  0.04  per  cent,  of  phosphorus  were 
used  to  standardize  the  permanganate  and  the  method  of  precipitation 
left  0.001  per  cent,  of  phosphorus  in  the  solution  it  is  obvious  that  while 
the  permanganate  so  standardized  would  give  satisfactory  results  on 
another  steel  of  about  the  same  phosphorus  content  it  would  give 
entirely  false  results  on  a  steel  containing  several  times  as  much  phos- 
phorus, as  the  ratio  between  the  phosphorus  remaining  in  solution  and 
that  precipitated  would  be  entirely  different.  Any  change  in  the  routine 
of  the  precipitation  of  the  phosphorus  will  also  obviously  require  a  re- 
standardization  of  the  permanganate. 

By  using  nitric  acid  of  sp.  gr.  1.13  as  a  solvent  the  separation  of  SiC>2 
is  prevented  and  nitration  is  rendered  unnecessary. 

Process  for  Steels. — Dissolve  2  grams  of  the  well-mixed  drill- 
ings placed  in  a  300  c.c.  Erlenmeyer  flask  in  70  c.c.  of  HNO3 
sp.  gr.  1.13  (made  by  mixing  4  parts  of  concentrated  HNOs 
and  9  parts  of  water).  Heat  to  boiling  to  expel  most  of  the  nitric 
oxide,  then  add  in  two  or  three  portions  8  to  10  c.c.  of  a  solution 
of  KMnO4,  12  grams  to  the  liter.  Boil  till  the  pink  color  dis- 
appears, then  add  a  solution  of  NaNC>2  drop  by  drop  till  the 
brown  precipitate  of  MnC>2  is  redissolved  and  the  solution  be- 
comes clear. 

Add  NH4OH  to  neutralize  the  greater  part  of  the  free  HNO3 
which  will  be  the  case  when  the  amber  color  disappears  and  to 
solution  grows  red;  then  add  sufficient  HNOs  to  bring  back  the 
amber  color.  Dilute  to  150  c.c.,  heat  to  80°C.  and  add  50  c.c. 
of  molybdic  acid  solution.  Agitate  for  five  minutes  by  shaking 
or  by  blowing  a  current  of  air  through  the  solution.  Allow  to 


DETERMINATION  OF  PHOSPHORUS  55 

stand  for  two  or  three  minutes  or  longer,  if  necessary  to  settle  the 
precipitate,  and  filter,  washing  as  in  the  preceding  process.  Set 
the  funnel  in  the  flask  in  which  the  precipitate  was  made  and  dis- 
solve the  precipitate  on  the  filter  in  NH4OH  (1  :  4)  using  alto- 
gether 20  c.c.  ;  then  wash  the  filter  well  with  water.  Add  50  c.c. 
of  H2SO4  (1:4),  dilute  to  150-200  c.c.  and  reduce  either  by  add- 
ing 10  grams  of  pulverized  zinc  and  heating  for  10  minutes  as  in 
the  Emmerton  method,  or  by  passing  the  dilute  solution  (200  c.c.,) 
through  the  zinc  reductor  as  described  in  the  iron  assay. 

Titrate  the  reduced  solution  with  KMn04  till  a  faint  pink  re- 
mains, not  disappearing  within  a  minute.  Calculate  the  per- 
centage of  phosphorus  from  the  strength  of  the  KMn04  solution 
and  the  number  of  cubic  centimeters  used. 

After  having  made  a  few  analyses  and  having  determined  the 
proper  amount  of  NH4OH  necessary  to  add  in  neutralizing  the 
excess  of  HN03,  time  may  be  saved  by  adding  this  amount  at 
once,  and  avoiding  the  working  back  with  HNOs.  The  solu- 
tion is  then  shaken  till  the  precipitate  redissolves,  diluted  to 
150  c.c.,  cooled  or  warmed  to  80°  and  the  phosphorus  precipitated 
by  molybdic  acid  solution. 

This  addition  of  the  proper  amount  of  NH4OH  is  not  only 
quicker  but  gives  more  satisfactory  results  than  by  determining 
the  proper  acidity  of  the  solution  each  time  by  the  depth  of  the 
amber  color,  since  this  color  varies  with  the  sample  of  steel, 
the  amount  of  sample  taken,  and  the  volume  and  temperature  of 
the  solution. 

The  yellow  precipitate  must  be  washed  free  from  iron  salts  or 
the  results  will  be  incorrect,  since  the  iron  if  washed  into  the 
flask  with  the  precipitate  will  dissolve  in  the  acid  and  be  reduced 
with  zinc  and  titrated  with  permanganate. 

TlTRATION  OF  THE  YELLOW  PRECIPITATE  WITH  STANDARD  ALKALI 

This  method  is  in  the  writer's  opinion  the  best  for  steels  or  samples 
low  in  phosphorus.  It  is  both  rapid  and  accurate.  It  avoids  the  reduc- 
tion and  consequent  uncertainty  as  to  the  oxide  produced.  The 
reaction  may  be  written  as  follows  : 


12MoO3, 

Na(NH4)HP04  +  11H2O. 


56  METALLURGICAL  ANALYSIS 

Hundeshagen  has  shown  that  23  molecules  of  NaOH  are  required 
to  neutralize  1  molecule  of  yellow  precipitate.  This  gives  a  ratio  of 
1  atom  of  phosphorus  to  23  molecules  of  NaOH  or  by  weight  31  of  P  to 
921.15  of  NaOH,  or  1 : 29.71.  The  alkali  solution  must  be  free  from 
carbonate  which  would  interfere  with  the  end  reaction.  The  best 
indicator  is  a  dilute  alcoholic  solution  of  phenolphthalein.  The  alkali 
solution  should  be  standardized  on  pure  yellow  precipitate  carefully 
dried  to  constant  weight  at  150°C.  As  this  substance  is  rather  hygro- 
scopic, it  should  be  redried  every  time  it  is  used. 

To  prepare  the  yellow  precipitate  for  standardizing,  precipitate  a 
dilute  solution  of  Na2HP04  by  an  excess  of  molybdic  acid  solution,  first 
acidifying  the  phosphate  solution  with  HNOs.  Wash  the  precipitate 
carefully  with  water  and  dry  it  as  directed.  Determine  the  phosphorus 
in  a  portion  of  it  gravimetrically.  It  should  contain  1.63  per  cent,  of 
phosphorus. 

Preparation  of  the  Solutions.  Standard  Sodium  Hydroxide 
and  Standard  Nitric  Acid. — One-tenth  normal  solutions  may  be 
used.  In  this  case  1  c.c.  NaOH  is  equal  to  0.000135  gram  phos- 
phorus. 

It  is  more  convenient  to  have  a  solution  of  such  a  strength  that 
1  c.c.  equals  0.0002  gram  phosphorus;  then  if  2  grams  of  steel  are 
taken  for  the  analysis,  each  cubic  centimeter  of  hydroxide  solution 
will  be  equivalent  to  0.01  per  cent,  of  phosphorus.  To  make 
such  a  solution,  proceed  as  follows: 

Dissolve  15.4  grams  of  NaOH  as  free  as  possible  from  Na2CO3 
in  about  200  c.c.  of  water.  Now  add  a  saturated  solution  of 
Ba(OH)2  as  long  as  a  precipitate  forms.  Filter  at  once  from  the 
BaCOs  and  dilute  to  2  liters.  This  solution  will  be  a  little  too 
strong.  Now  prepare  an  approximate  HNOa  solution  by  diluting 
20  c.c.  of  concentrated  HNOs  to  2  liters.  Fill  a  burette  with 
this  acid  and  titrate  it  carefully  against  10  c.c.  of  the  NaOH  solu- 
tion. Next  weigh  0.1226  gram  of  dry  yellow  precipitate  (equal 
to  0.002  gram  of  P)  into  a  beaker;  add  50  c.c.  of  water  and  10  c.c. 
of  the  NaOH  solution  which  should  dissolve  the  precipitate  to  a 
perfectly  clear  solution.  Now  add  3  drops  of  phenolphthalein 
solution  and  titrate  with  the  acid  till  the  color  vanishes.  The 
difference  between  the  acid  required  for  the  NaOH  and  that 
required  in  the  second  case  is  the  number  of  cubic  centimeters  of 
the  HNOs  equivalent  to  0.002  gram  phosphorus.  Now  add 
sufficient  water  to  the  dilute  nitric  acid  to  make  10  c.c.  exactly 


DETERMINATION  OF  PHOSPHORUS  57 

equal  to  0.002  gram  phosphorus.  Repeat  the  test  with  the  yellow 
precipitate  and  soda  solution,  using  double  the  amount  of  yellow 
precipitate  and  30  c.c.  of  soda.  If  the  nitric  acid  is  not  exactly 
right,  correct  it  by  further  dilution  and  repeat  the  test.  Finally 
dilute  the  soda  solution  until  it  is  exactly  equivalent  to  the  nitric 
acid. 

As  a  check  the  HN03  should  also  be  standardized  against 
pure  sodium  carbonate  (Na2CO3).  Proceed  as  follows:  Put  5 
grams  of  the  pure  salt  in  a  platinum  crucible,  cover  the  crucible 
with  a  lid  and  embed  the  crucible  nearly  to  the  top  in  a  sand 
bath  and  place  a  thermometer  in  the  sand  by  the  side  of  the 
crucible.  Heat  the  sand  bath  until  the  temperature  rises  to 
270-300°C.,  and  keep  it  at  that  temperature  for  a  half  hour. 
This  is  to  drive  out  all  moisture  without  decomposing  the  car- 
bonate. Cool  the  crucible  and  contents  in  a  desiccator.  Weigh 
out  0.265  gram  of  the  carbonate,  dissolve  in  20  c.c.  of  distilled 
water,  add  a  few  drops  of  methyl  orange  indicator  and  titrate 
with  the  nitric  acid  solution  until  its  color  becomes  distinctly 
red  when  compared  with  the  color  of  another  solution  of  the 
same  volume  containing  the  same  amount  of  methyl  orange  and 
a  little  sodium  carbonate.  If  the  nitric  acid  is  exactly  N/10, 
just  50  c.c.  should  be  required  for  the  titration. 

The  nitric  acid,  if  preserved  in  a  tightly  stoppered  bottle, 
keeps  its  standard  indefinitely,  but  the  soda  solution  will  slowly 
change  on  account  of  absorption  of  CO2  by  the  slight  excess  of 
Ba(OH)2  present  and  must  be  retested  against  the  acid  frequently. 
This  can  be  prevented  by  using  a  guard  tube  containing  soda- 
lime.  The  soda  solution  also  changes  strength  by  attacking  the 
glass.  This  is  avoided  by  paraffining  the  inside  of  the  bottle. 

In  standardizing  the  acid  and  alkali,  instead  of  taking  yellow 
precipitate  directly  a  sample  of  steel  of  known  phosphorus  con- 
tent may  be  weighed  out  and  treated  as  in  the  regular  process. 
It  is  well  to  finally  check  the  solution  in  this  way  in  all  cases. 

Phenolphthalein  Solution. — Dissolve  0.2  gram  of  the  indicator 
in  200  c.c.  of  95  per  cent,  alcohol. 

Methyl  Orange  Solution. — Dissolve  0.025  gram  of  the  sodium 
salt  in  100  c.c.  of  water  and  add  0.70  c.c.  of  N/10  HC1. 

Process  for  Steel. — Weigh  out  2  grams  of  the  well-mixed 
drillings  into  a  400  c.c.  Erlenmeyer  flask.  Add  70  c.c.  HN03, 


58  METALLURGICAL  ANALYSIS 

sp.  gr.  1.13.  Heat  till  the  metal  is  dissolved,  then  add  to  the 
boiling  solution  7  to  8  c.c.  of  a  solution  of  KMn04,  12  grams  to 
the  liter.  Boil  till  the  pink  color  disappears  and  a  precipitate 
of  Mn02  forms.  Then  add  a  little  pure  ferrous  sulfate,  sodium 
nitrite  or  tartaric  acid,  and  heat  till  the  solution  clears.  Remove 
from  the  burner,  add  NH4OH  until  the  amber  color  of  the  solu- 
tion darkens  distinctly  and  takes  a  reddish  tint.  Then  add 
enough  HNOs  to  restore  the  amber  color  to  the  solution.  Dilute 
to  150  c.c.  and  cool  or  warm  to  80°C.  Add  50  c.c.  of  molybdate 
solution  and  shake  five  minutes.  Filter,  and  wash  the  flask  and 
the  precipitate  several  times  with  dilute  MoOs  solution,  then 
with  1  per  cent.  KN(>2  solution  till  neutral.  Put  the  filter  con- 
taining the  precipitate  back  into  the  flask  in  which  the  precipita- 
tion was  made,  and  add  to  the  flask  and  its  contents  a  measured 
quantity,  usually  10  or  20  c.c.  of  standard  NaOH.  Dilute  to 
50  c.c.  with  CO2  free  water,  add  2  drops  of  phenolphthalein;  shake 
to  disintegrate  the  filter  and  dissolve  the  precipitate,  and  then 
titrate  the  excess  of  alkali  with  standard  acid.  The  difference 
between  the  number  of  cubic  centimeters  of  nitric  acid  equivalent 
to  the  soda  solution  used  and  that  required  in  the  titration  will  be 
the  nitric  acid  equivalent  to  the  phosphorus;  and  if  the  nitric 
acid  is  of  correct  strength  each  cubic  centimeter  will  represent 
0.01  per  cent,  of  phosphorus. 

When  this  method  is  applied  to  pig-iron  it  is  best  to  add  a 
gram  of  ammonium  persulfate  to  the  solution  when  the  iron  is  all 
dissolved  and  then  boil  to  destroy  the  combined  carbon.  Then 
filter  off  the  residue  and  add  permanganate  to  the  filtrate  and 
proceed  as  above. 

The  process  may  be  somewhat  shortened,  as  noted  before  in 
the  Emmerton  process,  by  determining  the  amount  of  NH4OH 
required  to  neutralize  the  excess  of  acid  and  adding  it  at  once, 
thus  avoiding  the  reacidifying  with  HNOs.  This  amount  can 
be  easily  ascertained  after  a  few  trials,  noting  the  amount  of 
NH4OH  used,  the  amount  of  HNOs  required  to  bring  it  back, 
and  then  determining  by  trial  how  much  NH4OH  is  needed  to 
neutralize  the  amount  of  acid  so  used  and  deducting  it  from  what 
was  originally  added. 

In  dissolving  yellow  precipitate  by  standard  alkali  always  keep 
the  liquid  cool  and  the  solutions  dilute,  as  ammonia  is  set  free 


DETERMINATION  OF  PHOSPHORUS  59 

in  the  reaction  and  is  liable  to  be  lost  by  volatilization  if  the 
liquid  is  concentrated.  This  would  cause  error  in  the  nitric  acid 
titration. 

REFERENCES  ON  THE  TITRATION  METHOD: 
J.  Anal,  and  App.  Chem.,  VI,  p.  82. 
J.  Anal,  and  App.  Chem.,  VI,  p.  204. 
J.  Anal,  and  App.  Chem.,  VI,  p.  242. 
Z.  Anal.  Chem.,  XXVIII,  p.  171. 
Stahl  u.  Eisen,  XXVI,  p.  297. 

THE  DETERMINATION  OF  PHOSPHORUS  IN  STEEL  CONTAINING 

VANADIUM 

The  presence  of  vanadium  in  steel  interferes  with  the  determination 
of  phosphorus  by  making  the  precipitation  with  the  molybdic  acid  in- 
complete and  the  precipitate  impure  with  vanadium.  The  following 
method  of  E.  W.  Hagmaier1  is  short  and  accurate. 

Process  of  Analysis. — The  sample  of  steel  is  dissolved  in  aqua 
regia,  evaporated  to  dryness  and  baked.  When  all  the  acid  is 
driven  off  it  is  then  taken  up  in  strong  hydrochloric  acid;  when 
complete  solution  is  obtained  the  silica  is  filtered.  The  filtrate 
is  then  reduced  with  sulphurous  acid.  When  entirely  reduced 
5  c.c.  of  acetic  acid  90  per  cent,  and  10  c.c.  of  saturated  cerium 
chloride  solution  are  added.  NH4OH  (about  1  part  concen- 
trated ammonia  to  3  of  water)  is  added  drop  by  drop  with  con- 
stant stirring,  until  turbidity  is  shown.  The  solution  is  then 
heated  to  boiling,  allowed  to  settle,  and  filtered.  The  cerium 
phosphate  will  filter  rapidly,  especially  through  a  black  ribbon 
paper.  The  precipitate  is  washed  five  or  six  times  with  hot 
water  and  then  dissolved  off  the  paper  with  hot  (1-1)  nitric  acid, 
and  the  phosphorus  precipitated  as  in  other  cases  with  ammonium 
molybdate. 

Notes  on  the  Method. — It  is  better  to  filter  off  the  silica  before 
precipitating  the  cerium  phosphate,  for  the  presence  of  the  silicon  causes 
the  cerium  phosphate  to  filter  slowly. 

The  point  where  most  caution  is  required  in  the  whole  method  is  in 
adding  the  NH4OH.  This  must  be  added  very  slowly,  for  if  too  large 

1  E.  W.  HAGMAIEH,  Mel.  Chem.  Kng.,  XI,  p.  28, 


60  METALLURGICAL  ANALYSIS 

an  amount  is  once  added  it  seems  impossible  to  obtain  proper  conditions 
by  coming  back  again  with  hydrochloric  acid.  If  by  accident  too  much 
NH4OH  is  added,  the  best  plan  is  to  filter  the  precipitate,  redissolve  it  in 
hydrochloric  acid,  pass  in  sulfur  dioxide,  and  reprecipitate  the  cerium 
phosphate. 

This  method  has  been  tried  with  vanadium  from  0.166  up  to  5  per 
cent,  and  it  has  been  found  that  in  all  cases  above  0.5  to  1  per  cent,  one 
reprecipitation  of  the  cerium  phosphate  should  be  made,  and  with  1  per 
cent,  to  5  per  cent,  vanadium  two  reprecipitations. 

Determination  of  Phosphorus  by  Measuring  the  Volume  of  the 
Yellow  Precipitate. — This  method  is  occasionally  used  for  furnace 
control  in  steel  plants.  It  requires  a  special  centrifugal  machine 
and  graduated  bulbs  with  small  collecting  tubes  for  the  precipi- 
tate. A  description  will  be  found  in  the  Journal  of  Analytical 
and  Applied  Chemistry,  Volume  IV,  page  13. 

With  practice  it  is  possible  to  estimate  small  percentages  of 
phosphorus  in  steel  by  judging  the  amount  of  the  yellow  precipi- 
tate as  it  collects  on  the  bottom  of  the  ordinary  precipitation 
flask.  Such  estimation  will  usually  serve  the  same  end  as  is  ac- 
complished by  the  centrifugal  apparatus. 

THE  DETERMINATION  OF  PHOSPHORUS  IN  FERRO-ALLOYS 

The  determination  of  phosphorus  in  these  samples  calls  for  special 
treatment.  Most  of  the  ferro-alloys  are  very  difficultly  soluble  in 
acids,  and  fusion  must  be  resorted  to  to  effect  decomposition. 

Process  for  Ferrotitanium  and  Ferrochrome. — Place  in  a 
platinum  crucible  20  grams  of  sodium  carbonate  thoroughly 
mixed  with  4  grams  of  potassium  nitrate.  Then  mix  in  1  gram 
of  the  powdered  sample  and  heat  to  fusion.  When  the  melt  is  in 
a  state  of  quiet  fusion,  keep  it  at  a  bright  heat  for  30  minutes 
longer.  Allow  to  cool,  transfer  the  cake  to  a  4-in.  casserole  and 
dissolve  in  hot  water.  If  any  titanium  is  present,  it  remains  in- 
soluble as  sodium  titanate.  Chromium,  sulfur,  phosphorus,  sili- 
con, and  manganese  go  into  solution  as  sodium  chromate,  sulfate, 
silicate,  and  manganate.  Filter  and  wash  thoroughly  with  a  hot 
dilute  sodium  carbonate  solution.  The  iron  stays  on  the  filter  as 
ferric  oxide  with  the  sodium  titanate.  To  the  solution  add  1 : 1 
HC1  until  it  is  slightly  acid.  Add  a  solution  of  ferric  chloride  con- 


DETERMINATION  OF  PHOSPHORUS  61 

taining  0.05  gram  of  iron,  add  NH4OH  until  the  solution  is  just 
alkaline,  then  acidulate  slightly  with  acetic  acid.  Boil  for  a  few 
minutes,  filter  and  wash  the  precipitate  of  ferric  phosphate  and 
hydroxide  with  hot  water.  Dissolve  the  precipitate  on  the  filter 
in  hot  dilute  HC1,  evaporate  the  solution  to  dryness,  redissolve 
in  a  few  drops  of  HC1,  dilute  to  70  c.c.,  filter  if  there  is  any  silica 
present,  add  5  c.c.  of  HN03,  then  NH4OH  until  just  alkaline. 
Now  add  3  c.c.  of  HN03,  heat  to  80°,  add  molybdic  acid  solution 
and  determine  the  phosphorus  as  usual. 

Phosphorus  in  Ferrotungsten. — Johnson  has  shown  that  the  method 
of  decomposing  high  tungsten  materials  by  fusion  with  sodium  car- 
bonate and  niter  and  leaching  out  the  fusion  with  water,  with  subse- 
quent separation  of  the  tungsten  by  evaporation  to  dryness  with  HC1 
gives  low  results.  He  gives  the  following  method  as  being  fairly  correct. 

Process  of  Analysis. — Dissolve  1  gram  of  sample  in  a  platinum 
dish  with  30  c.c.  of  HNO3  and  3  c.c.  of  HF.  The  sample  should 
dissolve  to  a  clear  solution  after  heating  to  boiling.  Transfer  to 
a  porcelain  dish  and  evaporate  to  dryness,  but  do  not  bake.  Dis- 
solve the  residue  in  50  c.c.  of  HC1,  sp.  gr.  1.2,  and  again  evaporate 
to  dryness,  without  baking.  Dissolve  the  residue  in  20  c.c.  of 
HC1,  heat,  add  50  c.c.  of  water,  heat  and  filter,  and  wash  with 
dilute  HC1.  Evaporate  to  10  c.c.,  add  20  c.c.  of  water,  filter  and 
wash.  Evaporate  to  10  c.c.,  add  75  c.c.  of  concentrated  HNO3, 
heat  until  all  action  is  over  and  evaporate  to  20  c.c.  Add  50  c.c. 
HNO3  and  again  evaporate  to  10  c.c.  Add  20  c.c.  of  water,  heat 
and  filter  and  wash  with  2  per  cent.  HNO3.  To  the  filtrate  add 
a  slight  excess  of  KMnC>4  and  carry  on  the  determination  of  the 
phosphorus  as  in  a  steel. 

REFERENCE : 

JOHNSON,  J.  Ind.  Eng.  Chem.,  V,  297. 

Process  for  Ferrosilicon  and  Ferro-manganese. — Fuse  as 
for  ferrotitanium,  dissolve  in  a  casserole  in  hot  water,  then  add 
HC1,  keeping  the  casserole  covered  with  a  watch-glass,  until  an 
excess  of  acid  has  been  added  and  everything  is  in  solution. 
Wash  off  the  cover  and  evaporate  to  dryness  on  a  water-bath. 
Add  10  c.c.  of  strong  HC1,  heat  until  the  iron  all  goes  in  solution, 
dilute  and  filter.  Now  add  ferric  chloride  to  the  solution,  and 
proceed  as  above, 


62  METALLURGICAL  ANALYSIS 

Process  for  Ferrovanadium. — As  has  been  mentioned  before, 
vanadium  precipitates  with  the  yellow  precipitate  and  further- 
more prevents  the  complete  precipitation  of  the  phosphorus,  so 
the  vanadium  must  be  separated  from  the  phosphorus.  The 
following  method  is  due  to  C.  M.  Johnson  (See  Chemical  Analysis 
of  Special  Steels  and  Steel-making  Alloys  and  Graphites,  page 
21).  Fuse  1  gram  of  sample  as  directed  above  for  ferrotitanium. 
Proceed  until  the  residue  is  obtained  on  the  filter  paper;  burn 
this  in  a  platinum  crucible  and  make  a  second  fusion  and  extrac- 
tion. The  combined  filtrates  and  washings  are  placed  in  a  large 
beaker  and  5  c.c.  of  sodium  aluminate  solution  is  added.  (Sod- 
ium aluminate  is  made  by  placing  10  grams  of  metallic  alumin- 
ium in  a  large  dish  with  50  grams  of  caustic  soda.  Water  is 
added  very  carefully  until  the  reaction  is  complete.  The  mass  of 
aluminate  is  dissolved  in  water,  filtered,  and  diluted  to  500  c.c.). 

HC1 1  : 1  is  added  until  the  solution  no  longer  changes  turmeric 
paper  at  once  to  even  a  faint  brown. 

Aluminium  hydroxide  and  phosphate  precipitate.  The  pre- 
cipitate is  filtered  and  washed  with  ammonium  nitrate  solution, 
roasted  in  a  platinum  crucible  and  again  fused  with  10  grams  of 
sodium  carbonate  and  2  grams  of  potassium  nitrate.  The  melt  is 
dissolved  in  water,  filtered  and  precipitated  again  with  1  :  1  HC1. 
This  precipitate  is  then  washed,  dissolved  in  5  c.c.  of  HN03, 
diluted  to  75  c.c.,  NH4OH  added  until  alkaline,  nitric  acid  added 
and  the  phosphorus  precipitated  and  estimated  as  usual. 

Determination  of  Phosphorus  in  Tungsten  Steel. — Dissolve  the 
sample  in  a  mixture  of  30  c.c.  of  HNO3  and  30  c.c.  of  HC1.  Heat 
until  action  ceases  and  the  residue  in  the  bottom  of  the  dish  is 
bright  yellow.  If  it  is  not,  repeat  the  addition  of  acid.  Now 
evaporate  to  a  small  volume,  add  50  c.c.  more  HNOs,  and  evap- 
orate to  hard  dryness,  finally  heating  nearly  to  a  red  heat.  Cool, 
add  50  c.c.  of  strong  HC1,  and  heat  until  the  residue  is  a  bright 
yellow  and  no  iron  is  left  undissolved.  The  residue  is  WOs,  SiC>2, 
with  small  amounts  of  iron  and  chromium.  Filter,  wash,  and 
evaporate  to  a  small  volume,  add  a  little  water  and  filter  to  re- 
move what  little  WOa  may  be  present.  In  the  filtrate  determine 
the  phosphorus,  as  in  the  case  of  any  steel. 


CHAPTER  V 

THE  DETERMINATION  OF  SILICON  IN  IRON 

The  metals  in  which  silicon  has  most  frequently  to  be  determined 
are  pig-iron,  containing  from  %  to 4  or  5  percent.;  "ferrosilicon,"  con- 
taining up  to  30  per  cent.,  steel  with  from  traces  to  1  per  cent,  and 
wrought  iron  with  small  fractions  of  1  per  cent. 

In  all  these  the  silicon  is  combined  as  Si,  not  as  SiO2,  though  there 
may  be  a  little  Si02  included  as  intermixed  slag,  especially  in  wrought 
iron. 

All  of  these  metals  are  soluble  in  HNOs,  sp.  gr.  1.2,  except  ferro- 
silicon,  the  silicon  being  oxidized  to  Si02,  which  passes  wholly  or  in  part 
into  solution.  Evaporation  of  the  HNOs  solution  to  dryness,  baking 
and  re-solution  in  HC1  renders  this  Si02  only  partially  insoluble,  a 
temperature  of  250°C.  not  causing  all  the  Si02  to  separate. 

To  accomplish  the  complete  separation  of  the  silica  by  this  means  it 
is  necessary  to  evaporate  to  dryness,  bake  as  in  the  phosphorus  deter- 
mination, dissolve  in  HC1,  and  again  evaporate  to  complete  dryness,  ex- 
pelling all  the  HC1.  On  taking  up  again  in  HC1  practically  all  of  the 
silica  is  left  insoluble.  After  dilution  the  solution  may  be  filtered  from 
the  residue  of  silica  +  carbon,  which  after  thorough  washing,  first  with 
HC  and  then  with  water,  may  be  ignited  till  the  carbon  is  burned  off, 
and  weighed. 

The  silica  thus  obtained  is  rarely  pure,  and  must  be  treated  with  H2S04 
and  HF,  or  must  be  fused  and  the  silica  separated  from  the  fusion. 
(See  analysis  of  limestones.) 

Hydrochloric  acid  or  aqua  regia  may  be  used  to  dissolve  the  metal 
instead  of  HN03,  but  they  do  not  attack  ordinary  iron  so  rapidly. 
Finally,  solution  in  H2S04  and  HNOs  and  evaporation  till  fumes  of 
H2S04  are  given  off  will  cause  a  complete  separation  of  the  silica. 

REFERENCES: 

For  details  of  these  various  methods  see — 

BLAIR,  "Chemical  Analysis  of  Iron,"  Nitric  Acid  Method. 

TROILIUS,  "Notes  on  the  Chemistry  of  Iron,"  p.  35,  Sulfuric  Acid 

Method. 

Also  Trans.  Am.  Inst.  Mining  Eng.,  X,  162,  et  seq.,  and  187,  et  seq. 

63 


64  METALLURGICAL  ANALYSIS 

When  a  nitric  or  hydrochloric  acid  solution  containing  silica  is 
evaporated  with  H2S04  the  volatile  acids  will  be  expelled,  and  if  the 
temperature  is  finally  raised  to  near  the  boiling-point  of  the  concen- 
trated acid,  the  silica  is  completely  dehydrated  and  becomes  insoluble. 
Titanic  acid,  if  present,  passes  into  solution  and  the  silica  thus  obtained 
is  pure.  The  following  method,  slightly  modified  from  one  published 
by  Dr.  Drown,  depends  upon  this  fact.  (Trans.  Am.  Inst.  Mining 
Eng.,  VII,  346.) 

Process  for  Pig-iron  and  Steel.— Weigh  out  0.9386  gram  of 
pig-iron  or  4.693  grams  of  wrought  iron  or  steel.  Put  into  a 
casserole  or  dish  and  cover  with  a  large  watch-glass.  Add 
carefully  30  c.c.  of  a  cold  mixture  of  8  parts  by  volume  of  con- 
centrated HNO3,  5  parts  of  concentrated  H2SO4  and  17  parts  of 
H2O  (for  the  pig-iron)  or  100  c.c.  of  a  mixture  of  35  parts  of 
concentrated  HNO3,  15  parts  of  H2SO4  and  50  parts  of  H2O  (for 
the  steel),  or  use  the  three-acid  mixture  given  further  on. 

Warm  till  action  ceases,  then  boil  down  rapidly  on  an  iron 
plate  or  over  the  bare  flame  until  the  Fe2(SO4)3  separates  as  a 
white  mass;  continue  the  heating  until  dense  fumes  of  sulfuric 
acid  are  evolved.  These  have  a  peculiar  suffocating  odor,  easily 
recognized.  Their  formation  indicates  the  total  expulsion  of 
the  HN03,  and  this  is  absolutely  necessary  in  order  to  make  the 
silica  insoluble.  In  the  case  of  steel  low  in  silicon  it  is  necessary 
to  stir  up  the  mass  of  ferric  sulf ate  thoroughly  or  it  may  include 
silica  not  dehydrated  and  so  cause  loss.  (DUDLEY).  There 
will  be  danger  of  " spattering"  unless  the  heating  is  carefully 
done,  but  if  the  dish  is  well  covered  this  need  cause  no  loss. 

Now  let  cool,  then  add  10  c.c.  of  concentrated  HC1  and  wash 
off  the  cover  into  the  dish.  Dilute  to  150  or  200  c.c.,  cover,  set 
over  a  burner  and  boil  until  all  Fe2(SO4)3  is  dissolved.  This  can 
be  recognized  by  the  disappearance  of  the  silky  precipitate  in 
the  liquid.  Continue  the  boiling  for  five  minutes,  as  this  will 
cause  the  solution  to  filter  more  easily.  Then  wash  off  the  cover, 
and  let  the  liquid  stand  until  all  the  silica  settles.  Decant  the 
clear  liquid  through  a  7-cm.  ashless  filter,  previously  washed  out 
with  boiling  water.  Finally  transfer  and  wash  the  residue  with 
hot  water.  When  partially  washed,  drop  a  little  HC1  on  the 
filter  and  residue,  then  wash  again  with  hot  water  till  the  filtrate 
no  longer  tastes  acid.  Without  drying  transfer  the  filter  to  a 


THE  DETERMINATION  OF  SILICON  IN  IRON  65 

crucible  and  ignite,  gently  at  first,  finally  at  high  heat,  until  all  the 
carbon  (graphite)  is  burned  and  the  silica  is  white.  If  this  is 
done  in  a  platinum  crucible  and  over  a  blast  lamp  the  burning 
off  of  the  carbon  need  not  take  more  than  a  few  minutes. 

It  is  important  that  the  temperature  be  low  at  first,  not  exceed- 
ing a  dull  red  until  the  paper  and  the  amorphous  carbon  are 
burned  out,  as  overheating  at  first  will  cause  the  carbon  to  lump 
together  and  it  will  then  burn  very  slowly.  During  the  final 
heating  over  the  blast  lamp  keep  the  crucible  partly  covered. 
The  burning  may  be  hastened  by  directing  a  gentle  current  of 
oxygen  gas  into  the  crucible,  but  if  due  care  is  taken  this  is  not 
necessary.  If  oxygen  is  used  take  care  not  to  blow  any  particles 
of  silica  out  of  the  crucible  by  forcing  in  the  gas  too  rapidly. 

The  weight  of  the  silica  in  milligrams  divided  by  2  in  the  first 
case  or  by  10  in  the  second  gives  the  silicon  in  tenths  of  a  per 
cent. 

Notes  on  the  Process. — If  the  above  directions  are  followed  exactly 
as  to  the  dilution  and  boiling  of  the  solution  there  will  be  no  need  of  a 
filter  pump  to  secure  rapid  nitration.  Boiling  with  a  large  excess  of 
water  consolidates  the  silica  so  that  it  filters  easily.  The  funnels  and 
filter  paper  should  be  carefully  selected;  the  former  should  have  long 
and  narrow  stems  that  will  fill  with  the  liquid  and  produce  a  little  suc- 
tion. The  funnel  angle  should  be  60  degrees.  A  porous  ashless  paper 
like  the  Muncktel  " black  label"  is  desirable.  The  precipitate  of  silica 
has  no*  tendency  to  run  through,  so  that  a  dense  paper  is  not  necessary. 

The  filter  should  be  kept  full  while  filtering  the  solution  as,  if  it  is 
allowed  to  empty,  the  paper  will  become  clogged. 

For  pig-iron  and  ferro-silicons  the  following  three-acid  silicon  mix- 
ture may  be  substituted  for  that  already  given,  and  will  be  found  very 
efficient: 

Water 150  c.c. 

Sulfuric  acid,  sp.  gr.  1.84 40  c.c. 

Nitric  acid,  sp.  gr.  14.2 80  c.c. 

Hydrochloric  acid,  sp.  gr.  1.19 60  c.c. 

Mix  in  the  order  given  and  preserve  for  use.  Twenty-five  cubic  centi- 
meters of  this  mixture  is  enough  for  the  "factor  weight"  of  pig-iron 
(0.4693  gram).  Evaporate  to  strong  fumes  of  H2S04,  cool,  add  a  little 
concentrated  HC1,  then  add  water  and  boil.  With  this  mixture  the 
silica  niters  particularly  well.  With  steel  where  the  silicon  is  in  very 


66  METALLURGICAL  ANALYSIS 

small  amount  it  is  necessary  to  test  its  purity.  Add  a  drop  of  H2S04 
to  the  silica  in  the  crucible  and  then  a  few  drops  of  pure  HF  or  a  few 
crystals  of  NH4F.  Evaporate  to  dryness  over  a  low  flame,  not  allow- 
ing the  liquid  to  boil,  and  ignite  the  residue  strongly.  The  fumes  of 
HF  are  poisonous,  so  the  evaporation  must  be  made  under  a  good  hood. 
The  silica  passes  off  as  volatile  SiF4.  If  any  residue  remains,  weigh 
it  and  deduct  it  from  the  total  weight.  The  difference  is  SiC>2. 

The  following  process  is  sometimes  used  for  furnace  control  instead 
of  the  one  just  given. 

The  molten  iron  is  chilled  by  pouring  into  water.  This  makes  it 
very  brittle.  It  is  then  pulverized  in  a  steel  mortar,  dissolved  in  HC1, 
rapidly  evaporated  to  dryness,  taken  up  in  HC1,  diluted  and  filtered. 
Without  drying,  the  filter  is  put  into  a  platinum  crucible,  ignited  in  a 
steam  of  oxygen  and  weighed.  The  time  required  for  this  process  is 
said  to  be  12  minutes. 

In  preparing  the  drillings  for  analysis,  great  care  must  be  taken  to 
keep  them  free  from  sand.  This  is  difficult  in  the  case  of  pig-iron, 
drillings  from  which  should  usually  be  cleaned. 

This  is  easily  accomplished  by  folding  a  sheet  of  paper  over  a  magnet, 
then  picking  up  the  metal  against  the  paper.  The  sand  and  other 
foreign  particles  are  left  behind.  On  drawing  the  magnet  away  from 
the  paper  the  drillings  will  fall  off  and  can  be  collected  on  a  clean  sheet 
of  paper.  All  the  drillings  must  be  gone  over  and  no  considerable 
residue  should  remain.  If  much  graphite-like  substance  is  separated 
it  may  hold  silicon  belonging  to  the  sample. 

The  drillings  should  be  fine.  Large  fragments  of  metal  dissolve 
slowly  and  may  be  left  as  hard  grains  in  the  silica,  of  course  vitiating 
the  result.  If  these  lumps  remain,  add  more  acid  and  heat  slowly  until 
they  dissolve. 

Ferro-silicons  may  need  to  be  pulverized  till  they  go  through  bolting 
cloth  before  they  will  dissolve. 

In  weighing  out,  great  care  must  be  taken  to  secure  an  average  of 
fine  and  coarse,  as  these  usually  differ  in  percentage  of  silicon. 

To  avoid  unnecessary  calculation  it  is  usually  convenient  to  weigh 
out  the  "f actor  weight"  of  the  metal.  Si02  contains  0.4693  Si;  hence, 
if  that  weight  in  grams  is  taken  for  the  analysis,  each  milligram  of  silica 
will  indicate  i^0  per  cent.  In  low  silicon  irons  or  steel  0.9386  or  some 
other  multiple  of  the  factor  may  be  used. 

Determination  of  Silicon  in  Ferro-silicon. — This  material  is 
not  easily  attacked  by  any  of  the  above  mixtures.  If  not  too 
high  in  silicon,  it  can  usually  be  dissolved  by  prolonged  boiling 


THE  DET  BUM  I  NAT  ION  OF  SILICON  IN  IRON  67 

with  aqua  regia,  adding  fresh  acid  from  time  to  time.  Finally 
add  25  c.c.  of  dilute  (1  :3)  H2SO4,  evaporate  until  fumes  of  sul- 
furic  acid  appear,  and  then  finish  as  in  the  regular  process. 

Samples  with  over  10  per  cent,  silicon  and  which  aqua  regia 
will  not  dissolve  are,  according  to  Williams,  best  treated  by  fusing 
with  six  or  eight  times  their  weight  of  dry  Na2CO3.  Then  pro- 
ceed with  the  fusion,  as  in  the  determination  of  silica  in  a  lime- 
stone. The  metal  must  be  very  finely  pulverized  and  not  more 
than  0.5  gram  taken.  (WILLIAMS,  Trans.  Am.  Inst.  Mining 
Eng.,  XVII,  542.) 

Instead  of  Na2CO3  alone,  a  mixture  of  Na2CO3  and  NaN03 
or  Na2O2  may  be  used  and  the  fusion  conducted  as  described  on 
page  60.  But  these  reagents  are  much  more  injurious  to  the 
platinum  than  the  carbonate,  though  more  fusible  and  more 
rapid  in  their  action. 

Determination  of  Silica  in  Admixed  Slag  in  Steel. — It  is  some- 
times necessary  to  distinguish  between  the  silicon  combined  in 
the  steel  as  silicide  and  that  combined  as  admixed  slag.  The 
following  method  depends  upon  the  fact  that  iron  is  dissolved 
with  iodine,  while  slag  is  unattacked.  Silica  formed  from  the 
silicide  is  soluble  in  caustic  soda. 

Process. — Place  5  grams  of  the  drillings  in  a  beaker,  put  the 
beaker  in  a  dish  filled  with  ice  or  snow  and  pour  over  the  drill- 
ings 25  c.c.  of  ice-cold  water.  Add  gradually  about  30  grams  of 
resublimed  iodine  stirring  until  the  iodine  is  all  dissolved.  Keep 
the  beaker  covered  with  a  glass  and  constantly  surrounded  with 
the  scraped  ice  or  snow.  Stir  the  solution  frequently,  until  the 
iron  is  all  dissolved.  Then  add  100  c.c.  of  cold  water;  allow  the 
insoluble  matter  to  settle  and  decant  the  liquid  through  a  small 
filter.  Wash  the  insoluble  residue  several  times  with  water  by 
decantation.  If  any  metallic  iron  remains,  give  the  residue  a 
further  treatment  with  iodine.  Transfer  the  insoluble  matter 
to  the  filter,  wash  once  with  1  :  20  HC1,  then  wash  well  with  water 
a  dozen  times.  Wash  the  residue  on  the  paper  back  into  a  plat- 
inum dish,  add  enough  NaOH  to  make  a  10  per  cent,  solution, 
and  heat  to  boiling  for  several  minutes.  This  dissolves  any 
precipitated  silica  formed  from  the  silicide  of  the  steel.  Decant 
the  liquid  through  a  small  filter,  and  again  boil  the  insoluble 
matter  with  50  c.c.  of  10  per  cent.  NaOH  solution.  Filter  this 


68  METALLURGICAL  ANALYSIS 

through  the  same  paper,  wash  several  times  with  hot  water, 
and,  finally,  wash  with  dilute  HC1  (1:20),  and  again  several 
times  with  hot  water.  Ignite  and  weigh  as  Slag  and  Oxide.  In 
this  then  determine  the  silica  as  in  a  steel. 


CHAPTER  VI 

THE  DETERMINATION  OF  MANGANESE 

There  are  two  classes  of  material  to  be  considered:  first,  ores,  slags 
and  metals  high  in  manganese,  such  as  manganite  and  ferro-manganese 
containing  from  15  to  90  per  cent.  Second,  ordinary  iron  ores,  pig- 
irons  and  steel,  containing  from  a  trace  up  to  about  3  per  cent,  of  man- 
ganese. These  call  for  a  somewhat  different  treatment. 

THE  ACETATE  PROCESS 

This  is  a  standard  process.  It  depends  upon  the  separation  of  the 
iron  from  the  manganese  as  a  basic  acetate.  The  precipitate  will  con- 
tain also  any  alumina,  titanic  acid  and  phosphoric  acid  present  in  the 
solution.  To  get  a  good  separation  it  is  essential  that  the  process  be 
conducted  very  precisely  in  respect  to  certain  details. 

The  reactions  are  as  follows:  When  Na2C03  is  added  to  the  solution 
containing  FeCl3,  MnCh  and  excess  of  HC1,  the  free  HC1  is  first  neu- 
tralized, then  the  Na2C03  begins  to  act  on  the  FeCl3,  forming  what  is 
practically  a  solution  of  ferric  hydroxide  in  ferric  chloride.  It  has  been 
shown  that  1  part  of  ferric  chloride  will  hold  in  solution  in  this  way  as 
much  as  10  parts  of  ferric  hydroxide,  perhaps  as  FexCly(OH)z. 

This  solution  is  very  dark  red  in  color  and  probably  contains  a  com- 
plex compound  in  which  the  chlorine  of  the  ferric  chloride  is  partly 
replaced  by  hydroxyl.  Upon  the  addition  of  sodium  or  ammonium  ace- 
tate the  chlorine  remaining  in  this  compound  is  replaced  by  the  acetic 
acid  radical  and  sodium  or  ammonium  chloride  is  formed  in  the  solution. 
When  the  solution  is  heated,  this  complex  substance  is  decomposed; 
the  iron  being  completely  precipitated  as  hydroxide  retaining  only  a 
little  acetic  acid.  This  is  the  so-called  basic  acetate  precipitate.  The 
solution  now  contains  free  acetic  acid.  If  exactly  the  right  amount  of 
sodium  acetate  has  been  added,  the  manganese  will  be  left  in  the  solution 
and  none  of  it  will  be  found  in  the  precipitate.  If  too  much  acetate  has 
been  added  some  manganese  dioxide  may  precipitate  with  the  iron. 
The  excess  of  sodium  acetate  has  the  effect  of  decreasing  the  acidity  of 
the  solution  by  introducing  a  lurgc  amount  of  the  acetate-ion,  thus 
decreasing  the  ionization  of  the  already  only  slightly  ionized  acetic  acid 

69 


70  METALLURGICAL  ANALYSIS 

set  free  by  the  hydrolysis  of  the  basic  acetate  of  iron.  This  decrease  in 
acidity  may  make  it  possible  for  the  Mn02  to  precipitate. 

From  these  facts  it  is  evident  that  as  much  sodium  carbonate  should 
be  added  as  possible  without  causing  a  permanent  precipitate,  and 
only  as  much  sodium  acetate  added  as  is  necessary  to  replace  the 
chlorine  remaining  in  combination  with  the  iron  and  make  the  proper 
acidity. 

The  dissociation  by  boiling  depends  upon  hydrolysis  and  is  only 
complete  in  very  dilute  solution;  at  least  500  c.c.  of  water  must  be 
present  for  each  gram  of  iron.  The  reaction  may  be  written: 

Fex(OH)y(CH3COO)z  +  ZHOH  =  XFe(OH)3  +  ZCH3COOH. 

THE   ACETATE   PROCESS   FOR   THE   DETERMINATION   OF   MAN- 
GANESE IN  ORES  WITH  HIGH  PERCENTAGES 

The  process  depends  upon  the  separation  of  the  iron  and  alumina 
as  basic  acetates,  precipitation  of  the  manganese  as  Mn02  by  bromine, 
resolution  of  the  precipitate  and  determination  of  the  manganese  as 
pyrophosphate. 

If  bromine  water  is  added  to  the  nitrate  from  the  basic  acetate,  the 
manganese  is  completely  precipitated  as  Mn02,  provided  an  excess  of 
sodium  acetate  over  that  required  to  convert  MnCl2  into  acetate  is  pres- 
ent. Nickel  and  cobalt,  if  present,  will  also  precipitate.  If  chromium  is 
present  some  will  stay  with  the  iron  and  some  will  go  with  the  manganese. 

If  ammonium  salts  are  present,  the  Mn02  will  only  separate  when  the 
solution  is  made  alkaline  and  then  not  completely.  The  iron  solution 
must  contain  no  ferrous  salt  or  a  red  " brick  dust"  like,  slimy  precipi- 
tate will  form,  and  the  nitrate  will  be  cloudy  and  deposit  iron. 

The  process  is  perfectly  satisfactory  provided  all  details  are  carefully 
followed. 

Process  for  Ores. — Dissolve  %  gram  of  the  ore  in  15  c.c. 
concentrated  HC1,  dilute  and  filter  as  in  the  iron  assay. 

Evaporation  to  dryness  is  usually  unnecessary,  few  ores  con- 
taining soluble  silicates.  When  such  occur,  as  in  slags,  dissolve 
in  dilute  acid,  evaporate  to  dryness,  add  HC1  and  then  water. 

If  no  chlorine  is  given  off  when  the  ore  is  dissolved,  owing  to 
the  absence  of  Mn02,  ferrous  iron  may  be  present.  In  this  case 
add  a  crystal  of  KC1O3  and  boil  until  all  the  chlorine  is  expelled. 

When  the  ferric  chloride  solution  is  evaporated  to  dryness  in 
the  presence  of  organic  matter,  a  slight  reduction  to  ferrous  salt 
often  occurs,  hence,  in  this  case  the  solution  should  be  oxidized 


THE  DETERMINATION  OF  MANGANESE  71 

after  filtration  by  adding  a  little  KC103  or  HNO3.  The  solution 
must  be  boiled  till  all  the  chlorine  is  expelled  or  manganese  will 
precipitate  with  the  iron  in  the  subsequent  separation. 

To  the  filtrate,  add  a  solution  of  sodium  carbonate  carefully 
until  a  slight  permanent  precipitate  forms.  Redissolve  this  with 
a  few  drops  of  HC1,  giving  each  drop  two  or  three  minutes  to  act, 
and  stopping  as  soon  as  the  solution  clears. 

Now  dilute  to  about  300  c.c.,  add  1  gram  sodium  acetate,  cover 
the  beaker  and  boil  vigorously  till  the  iron  separates.  Should  it 
not  come  down  promptly  add  a  solution  of  Na2CO3  drop  by  drop 
until  the  precipitation  is  complete.  The  liquid  must  be  distinctly 
acid  when  tested  by  a  slip  of  litmus  paper.  Let  the  precipitate 
settle  clear  and  decant  the  liquid  through  a  9  cm.  filter,  pouring 
off  as  closely  as  possible,  add  150  c.c.  of  boiling  water,  let  settle, 
decant  as  before,  and  finally  transfer  the  precipitate  and  wash 
once  with  hot  water.  Wash  it  off  the  filter  back  into  the  beaker. 
Dissolve  it  in  the  least  possible  quantity  of  HC1  and  repeat  the 
precipitation  exactly  as  before.  Transfer  the  precipitate  to  the 
filter  and  wash  well  with  hot  water.  Test  this  precipitate  for 
manganese  by  fusing  a  little  of  it  with  Na2CO3  and  NaNOs  on  a 
platinum  wire.  If  not  free  from  manganese  a  third  precipitation 
will  be  necessary;  or  the  manganese  in  the  precipitate  may  be 
determined  by  the  bismuthate-arsenite  method. 

The  filtrate  will  amount  to  about  a  liter.  It  should  be  per- 
fectly clear  and  colorless.  Concentrate  it  to  about  500  c.c.,  then 
add  10  grams  of  sodium  acetate  and  an  excess  of  bromine  water. 
Warm  until  the  MnO2  has  settled  and  the  liquid  is  clear.  Filter 
on  a  7  cm.  filter  and  wash  well  with  hot  water. 

Wash  the  precipitate  off  the  filter  into  a  beaker.  Now  wash 
the  filter  paper  with  dilute  HC1,  in  which  a  small  crystal  of  oxalic 
acid  is  dissolved,  receiving  the  filtrate  in  the  beaker  containing 
the  Mn02.  This  will  dissolve  any  MnO2  adhering  to  the  paper. 

Heat  the  beaker  containing  the  MnO2  and  HC1  and  add  oxalic 
acid  solution  drop  by  drop  until  the  MnO2  is  dissolved. 

Now  dilute  to  about  150  c.c.  and  add  NH4OH  until  the  solu- 
tion is  just  distinctly  alkaline,  putting  a  small  strip  of  litmus 
paper  in  the*  solution  as  an  indicator.  If  iron  is  present  a  slight 
precipitate  will  form.  Now  drop  in  acetic  acid  until  the  solu- 
tion is  just  acid.  Boil  the  solution.  If  any  precipitate  of 


72  METALLURGICAL  ANALYMX 

Fe(OH)3  separates,  filter  it  off  and  wash  precipitate  and  filter 
with  hot  water. 

Unless  this  precipitate  is  light  red  in  color  and  very  small  in 
amount,  dissolve  it  in  a  few  drops  of  HC1,  add  H20,  then  NH4OH, 
then  acetic  acid  as  before.  Boil  till  the  precipitate  separates 
and  filter  into  the  original  solution.  This  re-solution  is  essential 
in  most  cases,  and  need  delay  the  work  but  a  few  moments.  The 
object  of  the  oxalic  acid  is  to  reduce  the  MnO2  to  MnO,  and  so 
make  it  dissolve  quickly.  Mn02  is  very  slowly  attacked  by 
dilute  HC1  alone. 

To  the  filtrate,  now  perfectly  clear  and,  colorless,  add  an  excess 
of  a  solution  of  microcosmic  salt  (NaHNH4P04,4H2O).  Now 
heat  to  boiling,  add  NH4OH  drop  by  drop  as  fast  as  the  precipi- 
tate formed  by  each  addition  becomes  " silky"  in  appearance, 
stirring  all  the  time  to  prevent  bumping.  When  no  more  pre- 
cipitate forms  add  enough  NH4OH  to  make  the  solution  smell 
slightly  of  NH3,  and  boil  till  the  precipitate  is  completely  silky 
and  settles  quickly.  Now  cool  the  liquid  and  filter.  Wash  the 
precipitate  with  water  containing  a  few  drops  of  NH4OH.  Ignite 
and  weigh  as  Mn2P20?,  containing  0.3868  Mn. 

The  acetate  of  soda  used  must  be  tested  for  manganese.  If 
any  is  found,  dissolve  the  salt  in  water,  add  bromine  water  and 
boil  till  all  the  bromine  is  expelled.  Filter  the  solution  from  the 
MnO2  thus  separated  and  use  it  instead  of  the  solid  salt. 

Process  for  Spiegel  Eisen  and  Ferro-manganese.— Take  0.500 
gram  of  the  powdered  metal,  dissolve  in  10  c.c.  HNO3,  sp.  gr.  1.2, 
plus  5  c.c.  HC1,  evaporate  to  dryness  and  "bake,"  then  dissolve 
in  10  c.c.  of  concentrated  HC1,  add  a  little  bromine  water  (to 
reoxidize  any  FeO  formed),  boil  down  till  all  excess  of  bromine  is 
gone  and  most  of  the  HC1  evaporated.  Dilute,  filter  if  necessary 
and  precipitate  the  iron  and  determine  the  manganese  as  by  the 
method  for  ores. 

Some  ores  and  spiegel  irons  contain  copper  and  nickel.  These 
will  come  down  with  the  Mn02  in  part  at  least.  They  should 
be  separated  by  H2S,  which  will  precipitate  nickel,  cobalt,  copper 
and  zinc,  but  not  manganese  from  a  solution  containing  a  slight 
excess  of  acetic  acid.  This  may  be  done  in  the  original  acetate 
filtrate.  The  solution  must  be  boiled  till  all  H2S  is  expelled  be- 
fore adding  bromine. 


THE  DETERMINATION  OF  MANGANESE  73 

THE  ACETATE  PROCESS  FOR  ORES  Low  IN  MANGANESE 

In  this  case  it  is  desirable  to  work  upon  larger  amounts  of  material. 
The  nitration  and  washing  of  a  large  basic  acetate  precipitate  is  very 
troublesome,  and  can  be  avoided  by  taking  an  aliquot  part  of  the  solu- 
tion after  the  precipitate  has  settled.  The  error  introduced  by  neglect- 
ing the  volume  of  the  precipitate  is  inappreciable  when  the  percentage  of 
manganese  is  small. 

A  single  precipitation  of  the  iron  is  entirely  sufficient,  provided  care 
be  taken  to  avoid  excess  of  sodium  acetate. 

Extreme  care  in  measuring  the  solution,  as  well  as  in  keeping  the 
temperature  constant,  is  also  superfluous  when  less  than  3  per  cent,  of 
manganese  is  present  and  the  volumes  are  kept  large;  10  c.c.  on  a  liter 
causing  an  error  of  only  0.03  per  cent. 

The  precipitate  by  bromide  is  MnO2.  On  ignition  at  moderate 
temperatures  with  ample  access  of  air,  it  changes  principally  to  Mn304, 
though  the  exact  nature  of  the  oxide  produced  varies  with  the  condi- 
tions of  heating.  This  precipitate  also  usually  retains  small  amounts 
of  sodium  salts.  For  these  reasons  the  percentage  of  manganese  which 
it  contains  is  always  a  little  uncertain.  As  the  variations  are  limited  to 
a  small  percentage  of  the  weight  of  the  precipitate,  the  results  obtained 
by  weighing  it  directly  will  be  sufficiently  accurate  for  all  ordinary  work, 
where  but  little  manganese  is  present. 

Process  of  Analysis. — Dissolve  4  grams  of  the  ore  in  30  c.c. 
concentrated  HC1  exactly  as  in  the  iron  assay.  If  there  is  any 
ferrous  iron  present,  add  about  1  c.c.  of  HNO3  to  completely 
convert  it  to  ferric  chloride.  Boil  the  solution  until  the  excess  of 
HNOs  is  decomposed  and  the  chlorine  expelled.  The  evapora- 
tion need  not  go  so  far  that  insoluble  iron  salts  separate;  should 
such  form,  add  more  HC1  and  heat  until  they  dissolve.  Add 
water,  warm  and  filter  from  the  residue. 

Take  a  large  Erlenmeyer  flask,  one  which  will  hold  when  quite 
full  2400  c.c.  Dry  it,  then  measure  into  it  exactly  2000  c.c.  of 
water;  this  should  reach  up  into  the  narrower  portion  of  the  flask. 
Paste  a  thin  strip  of  paper  on  the  glass  to  exactly  indicate  the 
level  of  the  liquid.  The  flask  must  be  set  on  a  level  desk,  and  the 
place  it  stands  on  as  well  as  the  position  of  the  paper  mark  noted, 
so  that  it  can  be  subsequently  returned  to  the  same  position. 


74  METALLURGICAL  ANALYSIS 

Now  transfer  the  solution  of  the  ore  to  the  flask,  and  dilute 
it  to  about  1700  c.c.  Then  add  a  solution  of  Na2CO3  gradually 
until  the  liquid  begins  to  grow  dark  red.  Continue  to  add  the 
reagent  drop  by  drop,  shaking  the  flask  after  each  addition  until 
the  liquid  is  very  dark  in  color  and  the  precipitate  formed  redis- 
solves  very  slowly.  The  object  is  to  reach  a  point  just  short  of 
that  at  which  the  iron  is  precipitated.  The  operation  requires 
practice.  Should  the  point  be  overstepped,  add  a  little  HC1, 
and  when  the  liquid  becomes  clear,  neutralize  again;  but  in  this 
case,  in  the  writer's  opinion,  the  iron  precipitate  is  more  likely 
to  contain  manganese. 

Now  add  6  grams  of  pure  sodium  acetate.  Set  the  flask  on  a 
hot  plate  and  boil  the  solution  vigorously. 

The  iron  should  immediately  separate  as  a  bulky,  red  precipi- 
tate. If  it  fails  to  do  so  at  once,  drop  in  very  cautiously  a  dilute 
solution  of  Na2CO3  until  the  separation  is  complete.  Now  boil 
a  few  minutes  longer,  then  remove  the  flask  to  the  place  where  it 
stood  when  it  was  graduated,  placing  it  in  the  same  position,  and 
fill  it  exactly  to  the  mark  with  cold  water.  Stir  the  liquid 
thoroughly  with  a  long  rod,  then  let  it  settle.  As  soon  as  it  is 
clear  pour  off  1  liter  into  a  graduated  flask.  This  whole  operation 
can  be  done  so  quickly  that  the  liquid  will  not  cool  materially. 

Filter  the  measured  portion  of  the  liquid.  The  filtrate  should 
be  colorless  and  distinctly  acid  to  litmus  paper. 

Concentrate  the  filtrate  to  about  500  c.c.  Add  5  grams  of 
sodium  acetate  and  boil.  Should  any  precipitate  form  filter  it 
off,  dissolve  it  in  HC1  containing  a  little  oxalic  acid,  add  a  solution 
of  Na2CO3  until  a  slight  permanent  precipitate  forms,  then 
acetic  acid  till  just  acid.  Boil  this  liquid,  filter  from  any  pre- 
cipitate, and  add  the  filtrate  to  the  main  solution. 

Finally  add  bromine  water,  warm  until  the  MnO2  settles  com- 
pletely, filter,  wash  well  with  hot  water,  ignite  and  weigh  as 
Mn3O4  containing  0.7203  Mn.  Calculate  the  result  on  2  grams 
of  ore  taken. 

Should  the  ore  leave  but  little  residue  this  need  not  be  filtered 
off,  but  may  go  into  the  flask  with  the  solution.  In  applying 
this  process  to  slags  and  ores  containing  decomposable  silicates, 
the  HC1  solution  must  be  evaporated  to  dryness,  taken  up  again 
in  HC1,  HNOs  added  and  boiled  off  as  usual. 


THE  DETERMINATION  OF  MANGANESE  75 

If  care  be  taken  in  the  neutralizing  no  precipitate  will  form  on 
concentrating  the  filtrate  from  the  iron  and  delay  will  be  avoided. 

Should  the  ore  contain  nickel  or  cobalt,  these  will  contaminate 
the  manganese  precipitate  and  the  results  will  be  inaccurate. 
In  this  case  the  precipitate  of  MnO2  must  be  redissolved  in  HC1 
containing  a  little  sodium  sulfite.  The  solution  is  boiled  till  free 
from  S02,  then  cooled  and  nearly  neutralized  by  Na2C03,  a  little 
sodium  acetate  added  and  the  nickel  and  cobalt  precipitated  by 
H2S.  In  the  filtrate  from  these  sulfides  the  manganese  can  be 
determined  either  by  precipitation  with  bromine  or  as  phosphate. 

The  Acetate  Process  Applied  to  Pig-iron  and  Steel. — Dissolve 
4  grams  in  50  c.c.  HN03,  sp.  gr.  1.2,  add  10  c.c.  concentrated 
HC1.  Evaporate  to  dryness  and  bake.  Redissolve  in  25  c.c. 
concentrated  HC1,  add  a  little  HNO3,  boil  and  proceed  as  with 
ores  low  in  manganese.  Filtration  from  the  insoluble  residue  is 
unnecessary. 

REFERENCES  ON  THE  ACETATE  PROCESS: 

BLAIR,  "The  Chemical  Analysis  of  Iron." 
Trans.  Am.  Inst.  Mining  Eng.,  X,  p.  101. 
SILLIMANS,  Am.  J.  Sci.,  (11)  XLIV,  p.  216,  on  the  determination  as 

phosphate. 
Ber.,  1900,  p.  1019. 

THE   FORD-WILLIAMS   METHOD   FOR   MANGANESE   SEPARATION 

OF  MANGANESE  BY  CHLORATES 

When  potassium  or  sodium  chlorate  is  added  to  a  solution  of  man- 
ganese in  hot  concentrated  HNO3  the  manganese  is  all  precipitated  as 
Mn02.  To  secure  complete  and  rapid  precipitation  the  chlorate 
should  be  added  to  the  boiling  solution  in  successive  small  portions, 
the  HN03  must  be  in  large  excess  and  concentrated,  HC1  must 
be  absent,  and  there  must  be  at  least  as  much  iron  as  manganese  in 
the  solution.  The  precipitate  may  be  filtered  off  on  an  asbestos  filter 
and  washed  with  concentrated  HN03.  Mn02  is  entirely  insoluble  in 
cold  concentrated  HN03  provided  this  contains  no  lower  oxides  of 
nitrogen  ("red  fumes");  if  these  are  present,  that  is,  if  the  HN03  is 
not  perfectly  colorless,  the  Mn02  will  be  reduced  and  dissolved. 

After  washing,  the  precipitate  may  be  redissolved  and  the  manganese 
determined  gravimetrically  as  pyrophos'phate  or  volumetrically  by 
measuring  the  oxidizing  power  of  the  Mn02  on  ferrous  sulphate  or  oxalic 
acid. 


76  METALLURGICAL  ANALYSIS 

The  precipitate  contains  a  little  iron  but  is  free  from  other  impurities. 

When  the  solution  to  which  the  chlorate  is  added  contains  any  HC1, 
this  is  first  acted  upon  and  broken  up  before  the  Mn02  will  separate, 
chlorine  being  driven  off  and  water  formed  by  the  oxidation.  This 
will  result  in  weakening  the  HN03,  and  hence  in  this  case  more  HNOa 
must  be  present  to  prevent  too  great  loss  of  strength. 

The  method  is  especially  adapted  to  the  determination  of  manganese 
in  steels  and  irons  low  in  silicon  and  dissolving  in  HNOs  without  residue. 

If  Si02  is  present  in  the  solution  it  may  separate  in  a  gelatinous 
form  which  prevents  filtration  and  coats  the  particles  of  the  precipitate 
so  that  they  dissolve  with  difficulty.  It  should  be  removed  by  the 
addition  of  a  few  drops  of  hydrofluoric  acid  to  the  liquid  after  the  pre- 
cipitation of  the  MnC>2.  Sodium  chlorate  is  preferable  to  potassium 
chlorate  because  its  greater  solubility  makes  it  easier  to  wash  out 
of  the  precipitate. 

Process  for  Steel  Low  in  Silicon. — Dissolve  5  grams  in  60  c.c. 
HNO3,  1.2  sp.  gr.,  in  a  200  c.c.  beaker.  Evaporate  to  25  c.c., 
then  add  100  c.c.  of  colorless  concentrated  HNO3.  Set  on  an  iron 
plate  and  heat  to  incipient  boiling.  Now  drop  in  powdered 
NaClOs  or  KClOs,  a  little  at  a  time,  adding  each  portion  when 
the  effervescence  produced  by  the  preceding  portion  has  ceased. 
By  the  time  2  to  2J^  grams  have  been  added  the  Mn(>2  will  have 
separated  as  a  fine  brown  powder.  Now  add  J£  gram  more  of  the 
chlorate  and  boil  gently  for  10  minutes.  If  any  SiC>2  is  present 
in  the  solution,  after  three  or  four  minutes  boiling  add  a  few  drops 
of  pure  HF.  Then  add  1  gram  more  of  the  chlorate  and  25  c.c. 
concentrated  HN03  and  boil  10  minutes  longer.  Remove  from 
the  plate  and  cool  by  setting  the  beaker  in  water.  When  the 
MnO2  has  settled,  filter  without  dilution,  through  an  asbestos 
filter  in  a  Gooch  crucible.  Finally  transfer  the  MnC>2  to  the 
filter  and  wash  beaker  and  filter  with  colorless  concentrated  HNOs 
three  or  four  times,  or  until  the  filtrate  is  colorless.  This  can  be 
done  without  using  more  than  15  or  20  c.c.,  adding  only  a  little 
each  time  and  letting  each  portion  run  through  before  adding 
the  next.  Finally  wash  with  a  little  cold  water.  If  the  HNOs 
is  colored  by  lower  oxides  of  nitrogen  (from  standing  and  the 
action  of  light),  it  can  be  purified  by  blowing  a  strong  current  of 
air  through  it  until  it  becomes  colorless. 

After  washing  the  MnO2  with  cold  water  till  the  acid  taste  is 
gone  from  the  filtrate  (letting  .each  successive  portion  of  water 


THE  DETERMINATION  OF  MANGANESE  77 

run  entirely  through  before  adding  the  next,  so  as  to  not  use  in 
all  more  than  20  c.c.)  wash  the  asbestos  and  precipitate  back 
into  the  beaker  (which  always  has  some  Mn02  adhering  to  it). 

Volumetric  Determination  of  the  Mn. — This  process  consists  in 
dissolving  the  Mn02  in  a  measured  excess  of  an  acid  solution  of  ferrous 
sulfate  of  a  known  strength.  Each  molecule  of  Mn02  changes  two 
molecules  of  ferrous  sulfate  to  ferric  sulfate.  The  amount  of  fer- 
rous sulfate  remaining  is  then  determined  by  a  standard  solution  of 
potassium  permanganate.  The  reactions  are  as  follows: 

1.  Mn02+2FeS04+2H2S04  =  MnS04+Fe2(S04)3+2H2O. 

2.  10FeSO4+2KMnO4+8H2S04  =  5Fe2(SO4)3  +  K2S04  +  2MnS04  + 

8H20. 

The  process  requires  first,  a  solution  of  potassium  permanganate  of 
a  known  strength;  second,  a  solution  of  ferrous  sulfate  in  dilute  sul- 
furic  acid.  The  strength  of  this  is  determined  by  titration  with  the 
permanganate  solution. 

Preparation  of  the  Permanganate  Solution. — Dissolve  1.151 
gram  of  pure  KMn04  in  water  and  dilute  to  1  liter.  One  cubic 
centimeter  of  this  solution  will  have  the  same  oxidizing  power 
as  0.001  gram  of  manganese  in  the  form  of  the  brown  precipitate 
(MnO2).  Check  the  solution  against  pure  iron  or  pure  ammon- 
ium ferrous  sulfate  (NH4)2Fe(SO4)26H20.  Dissolve  0.1425  gram 
of  the  salt  in  50  c.c.  of  water  containing  2  c.c.  of  H2SO4.  This 
should  consume  just  10  c.c.  of  the  permanganate  solution.  Run 
in  the  solution  until  the  last  drop  gives  a  permanent  pink  color. 

If  more  or  less  than  10  c.c.  is  required,  calculate  the  amount 
of  Mn  to  which  each  cubic  centimeter  of  the  permanganate  is 
equivalent  by  the  proportion,  0.001  :x  =  n :  10,  n  being  the 
number  of  cubic  centimeters  of  solution  used  in  the  test,  and 
x  the  required  value. 

Preparation  of  the  Ferrous  Sulfate  Solution. — Dissolve  20.18 
grams  of  pure  crystallized  ferrous  sulfate  (FeSO47H2O)  in  about 
500  c.c.  of  water,  to  which  25  c.c.  of  concentrated  H2S04  has  been 
added,  and  then  dilute  to  1  liter. 

Determine  its  strength  against  the  permanganate  solution  by 
measuring  15  c.c.  with  a  pipette  into  a  beaker,  adding  about 
25  c.c.  of  water  and  1  c.c.  of  H2SO4  and  then  running  in  the  per- 
manganate till  the  pink  color  is  permanent.  About  30  c.c. 
should  be  required.  This  value  must  be  determined  frequently 


78  METALLURGICAL  ANALYSIS 

as  the  solution  of  ferrous  sulfate  alters  rapidly  from  the  oxidizing 
action  of  the  air.  In  large  amounts  it  is  best  kept  in  a  carboy 
and  covered  with  a  layer  of  kerosene  oil  to  keep  out  air.  The 
solution  can  be  preserved  in  this  way  for  some  time  with  but 
little  alteration,  and  can  be  drawn  out  by  a  siphon  as  needed. 

From  the  two  formulas  already  given  we  have  the  relations 
between  the  MnO2,  FeSO4  and  KMnO4  as  follows: 

One  atom  of  Mn  in  the  form  of  brown  precipitate  (Mn02)  will 
oxidize  two  atoms  of  Fe  as  ferrous  sulfate.  Two  molecules  of 
permanganate  will  oxidize  ten  atoms  of  Fe  as  ferrous  sulfate, 
that  is  to  say,  two  molecules  of  permanganate  will  oxidize  the 
same  amount  of  iron  as  will  five  molecules  of  MnO2  containing 
five  atoms  of  manganese.  Therefore,  to  find  how  much  KMnO4 
will  be  needed  to  have  the  same  oxidizing  power  as  0.001  gram 
of  Mn  in  the  form  of  the  brown  precipitate  we  have  the 
proportion : 

5  atoms  Mn  :2  mol.  KMn04  =  275  :  316.3  =  0.001  :  x,  which 
gives  X  =  0.001 15  gram,  the  amount  of  KMnO4  to  be  dissolved 
in  1  c.c.  if  1  c.c.  is  to  be  equivalent  to  0.001  gram  Mn  as  "  brown 
precipitate."  This  is  1.151  gram  in  a  liter. 

To  determine  the  amount  of  iron,  or  of  ammonium  ferrous 
sulfate  to  which  1  c.c.  is  equivalent,  we  have: 

1  atom  Mn:2  atoms  Fe  =  55  : 112  =  0.001  :x,  in  which  x  is 
the  required  amount  of  iron.  The  value  of  x  is  0.002034.  To 
determine  the  amount  of  the  ammonium  ferrous  sulfate,  as  this 
contains  one-seventh  of  its  weight  of  iron,  multiply  the  value  of 
x  by  7  =  0.01425  for  1  c.c.,  or  the  figure  given  in  the  directions 
for  10  c.c. 

That  15  c.c.  of  the  ferrous  sulfate  solution  may  be  equivalent 
to  30  c.c.  of  the  permanganate  it  must  contain  0.06102  Fe.  This 
corresponds  to  20.18  grams  of  FeSO4,  7H2O  to  the  liter. 

Determination  of  the  MnO2. — To  the  asbestos  and  Mn02  in 
the  beaker,  add  the  solution  of  ferrous  sulfate  from  a  burette 
5  c.c.  at  a  time  until,  after  stirring  and  warming,  the  MnO2  is 
completely  dissolved.  It  is  best  to  take  the  same  burette  used  in 
standardizing.  Break  up  all  lumps  of  asbestos  and  precipitate 
with  a  glass  rod  as  they  may  inclose  undissolved  particles  of 
MnO2.  Now  add  a  little  water  and  run  in  the  permanganate 
solution  till  a  pink  color  is  produced,  not  disappearing  under  two 


THE  DETERMINATION  OF  MANGANESE  79 

or  three  minutes.  Read  the  burette  and  deduct  the  amount 
used  from  that  to  which  the  amount  of  ferrous  sulfate  taken 
would  have  been  equivalent;  the  difference  is  equivalent  to  the 
Mn  present  in  the  precipitate.  This,  corrected  by  the  factor  for 
the  permanganate  solution,  will  give  the  amount  of  Mn  in 
milligrams. 

As  an  example:  Suppose  that  5  c.c.  of  ferrous  sulfate  solution  equaled 
9.6  c.c.  of  permanganate  solution,  and  10.3  c.c.  permanganate  equaled 
0.1425  gram  of  ammonium  ferrous  sulfate.  If  15  c.c.  of  ferrous  sul- 
fate solution  were  added  to  dissolve  the  Mn02  and  the  permanganate 
required  to  oxidize  the  excess  was  4.5  c.c.,  then  the  calculation  is  as 
follows : 

3X9.6  =  28.8  =  the  permanganate  equivalent  to  the  FeSO4  used. 
4.5  =  the  "titer  back." 

24.3  =the   number   of    cubic    centimeters    of    permanganate 

equivalent  to  the  precipitate. 

24.3  :x  =  10.3  : 10  (x  being  the  true  amount  of  correct  permanganate). 
x  =  23.6  =  0.0236  gram  Mn  in  the  precipitate. 

Process  for  Ores. — Take  5  grams.  Dissolve  in  50  c.c.  of  con- 
centrated HC1,  evaporate  to  dryness,  avoiding  a  temperature 
above  100°;  add  20  c.c.  HC1,  and  then  water.  When  dissolved, 
filter  into  a  No.  2  beaker.  Add  50  c.c.  concentrated  HN03, 
evaporate  to  a  syrup,  then  add  100  c.c.  of  concentrated  HNO3 
and  proceed  as  before. 

Process  for  Pig-iron. — Dissolve  5  grams  of  the  metal  in 
HNO3,  sp.  gr.  1.2,  taking  about  60  c.c.  Then  add  25  c.c.  HC1, 
evaporate  to  dryness  and  bake.  Dissolve  in  HC1,  filter  from  the 
SiO2,  and  to  the  filtrate  add  0.2  gram  ammonium  fluoride  or  a 
few  drops  of  hydrochloric  acid.  Then  add  50  c.c.  of  HN03. 
Concentrate  to  a  syrup,  add  100  c.c.  HNO3  and  proceed  as  before. 
The  hydrofluoric  acid  expels  traces  of  SiO2  from  the  solution 
and  greatly  accelerates  the  filtration  from  the  Mn02  (E.  F. 
WOOD). 

The  above  process,  carefully  conducted,  is  capable  of  giving 
very  accurate  results,  but  it  requires  practice  and  should  be  tried 
on  metals  in  which  the  manganese  has  been  carefully  determined 
by  another  method  until  the  two  give  concordant  results. 


80  METALLURGICAL  ANALYSIS 

Process  for  Ferro  Manganese  and  Ores  High  in  Manganese.— The 
permanganate  solution  should  be  standardized  by  working  on  a  metal  of 
known  percentage  of  manganese,  as  the  composition  of  the  precipitate 
is  considered  by  some  chemists  not  to  be  exactly  Mn02,  but  by  thus 
standardizing  in  the  same  way  that  the  ore  is  analyzed,  all  risk  from  this 
source  is  avoided.  Where  only  small  amounts  of  manganese  are  pres- 
ent this  source  of  error  is  unimportant. 

The  Volhard  process,  however,  is  better  adapted  to  high  manganese 
materials  and  is  more  rapid. 

One  slight  objection  to  the  chlorate  process  is  the  large  amounts  of 
expensive  acids  required.  To  avoid  this  the  process  can  be  worked  on 
smaller  amounts  of  substance,  but  great  care  and  skill  are  then  needed 
to  secure  close  results.  All  measurements  and  titrations  must  be  very 
exact. 


Process. — Take  1  gram  of  iron  or  steel,  dissolve  it  in  15  c.c. 
of  HNO3,  sp.  gr.  1.2.  Evaporate  to  10  c.c.,  add  35  c.c.  HN03, 
sp.  gr.  1.42,  and  after  precipitation  and  boiling,  10  c.c.  more,  re- 
duce the  KC1O3  to  about  1  gram,  filter,  wash  and  proceed  with  the 
volumetric  determination  of  the  precipitate. 

It  is  possible  to  determine  the  MnO2  in  the  presence  of  the 
nitric  acid  without  filtering  it  off  by  proceeding  as  follows: 
After  precipitating  the  Mn02,  cool  the  acid  and  dilute  it  to  about 
400  c.c.  with  cold  water.  Now  add  the  ferrous  sulfate  solution  to 
dissolve  the  MnO2  directly,  and  immediately  titrate  with  the 
permanganate.  In  working  in  this  way  the  excess  of  potassium 
chlorate  must  be  completely  destroyed  before  diluting  the  solu- 
tion and  the  temperature  of  the  liquid  kept  quite  low  when 
adding  the  ferrous  sulfate.  Great  care  in  these  points  is  neces- 
sary in  order  not  to  start  the  reaction  between  the  HNO3  and 
the  FeSO4  which  would  vitiate  the  results.  The  permanganate 
solution  should  be  standardized  under  similar  conditions. 

REFERENCES  : 

Trans.  Am.  Inst.  Mining  Eng.,  IX,  p.  397. 

Trans.  Am.  Inst.  Mining  Eng.,  X,  p.  100. 

Trans.  Am.  Inst.  Mining  Eng.,  XII,  p.  73. 

Trans.  Am.  Inst.  Mining  Eng.,  XIV,  p.  372. 

J.  Am.  Chem.  Soc.,  1898,  p.  504. 

Am.  J.  Sci.,  V,  (4)  260. 

J.  Anal  App.  Chem.,  II,  p.  249. 


THE  DETERMINATION  OF  MANGANESE  81 

VOLHARD'S  PROCESS  FOR  MANGANESE 

This  is  a  volumetric  process  depending  upon  the  reactions  between 
potassium  permanganate  and  manganous  salts  by  which  all  the  manga- 
nese is  precipitated  as  MnC>2. 


The  method  is  especially  applicable  to  high  manganese  ores.  For 
low  manganese  ores  and  for  iron  and  steels  the  bismuthate-arsenite 
method  is  best. 

The  solution  must  be  neutral  or  very  nearly  so.  The  titration  must 
be  made  with  the  solution  nearly  at  the  boiling-point  and  very  dilute  or 
the  precipitate  will  not  settle  quickly  and  it  will  be  difficult  to  see  the 
end  reaction.  For  the  same  reason  the  solution  must  be  vigorously 
shaken  or  stirred  and  the  permanganate  added  rather  slowly,  especially 
at  first.  Too  rapid  addition  of  the  permanganate  will  cause  the  Mn02 
to  precipitate  on  the  glass,  forming  a  firmly  adherent  yellow-brown 
stain  which  makes  it  very  difficult  to  see  the  final  pink  color  produced 
by  the  excess  of  permanganate  when  the  titration  is  finished. 

The  permanganate  solution  used  in  the  iron  assay  will  serve  for 
manganese.  If  1  c.c.  equals  0.01  Fe,  then  1  c.c.  will  equal  0.002951  Mn. 

In  this  process  the  iron  is  separated  from  the  manganese  by  means  of 
zinc  oxide.  ZnO  precipitates  the  iron  completely  as  hydroxide  from 
a  dilute  solution  of  ferric  sulfate,  while  manganese  sulfate  is  not  affected 
and  remains  in  the  solution. 

Sufficient  ZnO  must  be  added  to  neutralize  any  free  sulfuric  acid 
present  as  well  as  to  precipitate  the  iron. 

The  separation  of  the  iron  is  really  due  to  hydrolysis,  the  ZnO  serving 
to  keep  the  solution  neutral.  The  reaction  is: 

Fe2(S04)3+3ZnO+6HOH  =  2Fe(OH)3+3ZnSO4+3H2.O 

The  ZnO  must  not  contain  any  alkali,  as  Na2COs,  as  this  would  precipi- 
tate manganese. 

Process  for  Ores.  —  Take  0.5  gram  of  the  sample;  ignite  it  to 
redness  if  carbonaceous  matter  is  present;  then  transfer  it  to  a 
casserole  and  digest  with  15  c.c.  of  concentrated  HC1.  If  any 
ferrous  iron  is  present  add  a  few  small  crystals  of  KC103  to  oxidize 
it  to  the  ferric  state.  Finally  boil  until  all  free  chlorine  is  ex- 
pelled. Now  add  10  c.c.  of  dilute  H2SO4  (1:1)  and  evaporate 
till  fumes  of  H2SO4  begin  to  come  off,  then  cool  the  casserole  and 
add  75  c.c.  of  water.  Warm  till  all  of  the  ferric  sulfate  goes  into 
solution  and  then  transfer  to  a  200  c.c,  graduated  flask. 


82  METALLURGICAL  ANALYSIS 

Add  a  solution  of  Na2C03  to  the  contents  of  the  flask  until 
most  of  the  free  acid  is  neutralized,  cool  the  contents  of  the 
flask  if  at  all  warm  and  then  add  ZnO  suspended  in  water, 
small  portions  at  a  time  and  shaking  after  each  addition,  till 
the  iron  separates  as  hydroxide.  Dilute  to  200  c.c.  and  mix 
thoroughly.  Let  the  precipitate  settle  and  then  filter  through 
a  dry  filter.  Collect  100  c.c.  of  the  filtrate  rejecting  the  first 
few  cubic  centimeters  that  run  through.  Transfer  this  portion 
to  a  large  flask,  dilute  it  to  300  c.c.,  add  exactly  two  drops  of 
HNO3,  sp.  gr.  1.2,  and  heat  to  boiling.  Titrate  with  KMnO4 
shaking  well  after  each  addition,  till  a  faint  pink  remains,  which 
does  not  disappear  for  a  few  minutes.  From  the  strength  of  the 
KMnO4  and  the  number  of  cubic  centimeters  required,  calculate 
the  percentage  of  Mn. 

The  titration  must  be  made  rapidly  so  that  it  will  be  finished 
before  the  solution  cools.  If  by  accident  the  solution  cools  so 
that  the  Mn02  separates  badly  before  finishing  the  titration, 
heat  it  again  quickly  but  not  to  boiling. 

Run  a  blank  on  the  reagents  to  test  them  for  manganese  or 
any  other  substance  which  would  reduce  the  KMnO4  solution. 

Process  for  Pig-iron  and  Steel. — Weigh  out  1  gram  of  the  well- 
mixed  borings  into  a  casserole.  Add  gradually  25  c.c.  of  HNO3, 
sp.  gr.  1.2.  When  the  metal  is  dissolved  evaporate  to  dry  ness 
and  bake  for  a  few  minutes,  then  take  up  in  10  or  15  c.c.  of  HC1 
and  heat  till  the  iron  salts  go  into  solution.  Now  add  10  c.c. 
of  dilute  H2SO4  (1:1)  and  evaporate  till  dense  fumes  of  H2SO4 
are  given  off,  keeping  the  dish  well  covered  to  avoid  loss  from 
spattering,  and  to  avoid  the  formation  of  dry  salts  on  the  sides 
of  the  casserole.  Cool,  add  100  c.c.  of  water,  and  warm  till  all 
the  ferric  sulfate  goes  into  solution.  Transfer  to  a  500  c.c. 
flask,  nearly  neutralize  with  Na2C03,  cool,  and  then  add  the 
zinc  oxide,  suspended  in  water  as  described  before,  till  the  iron 
is  precipitated.  Dilute  to  500  c.c.  mixing  the  contents  of  the 
flask  thoroughly.  Filter  off  250  c.c.  Add  to  this  two  drops 
of  HN03,  sp.  gr.  1.2,  heat  to  boiling  and  titrate  carefully  with 
KMn04  till  a  faint  pink  color  is  permanent. 

Notes  on  the  Process.— Where  the  amount  of  manganese  in  the  sample 
is  less  than  0.7  or  0.8  per  cent,  the  process  is  not  satisfactory,  unless  more 
of  the  sample  is  taken,  since  the  precipitate  will  not  clot  and  settle 


THE  DETERMINATION  OF  MANGANESE  83 

properly  if  there  is  less  than  5  or  6  mg.  of  manganese  in  the  liquid. 
Therefore,  in  applying  the  process  to  ores  or  metals  quite  low  in  manga- 
nese, enough  sample  must  be  weighed  out  so  that  there  shall  be  at  least 
this  amount  of  manganese  in  the  liquid  titrated. 

As  more  than  a  trace  of  free  acid  interferes  with  the  titration,  the 
amount  of  HNOs  added  must  not  exceed  that  indicated  or  the  precipi- 
tate will  settle  badly  and  the  end  point  be  indistinct.  Evaporation 
with  H2S04  is  necessary  to  destroy  the  carbonaceous  matter  as  well  as 
to  expel  the  HN03,  both  of  which  may  affect  the  titration. 

Instead  of  taking  1  gram  for  the  analysis,  it  is  usually  more  conven- 
ient to  take  such  an  amount  of  the  sample  as  will  make  1  c.c.  of  the 
permanganate  equivalent  to  1  per  cent,  of  manganese.  This  amount 
can  be  calculated  from  the  iron  standard  of  the  permanganate.  Thus, 
if  1  c.c.  of  the  KMn(>4  equals  0.01  Fe,  take  0.5902  gram  of  the  sample 
for  the  process,  then  the  half  of  the  solution  taken  for  the  titration  will 
contain  0.2951  gram  of  the  sample  and  each  cubic  centimeter  of  per- 
manganate used  will  obviously  represent  1  per  cent,  of  Mn. 

For  steels  low  in  carbon  the  Volhard  method  has  been  modified  by 
omitting  the  evaporation  with  H2S04  and  not  filtering  from  the  precipi- 
tate of  ferric  hydroxide  produced  by  the  ZnO,  but  instead  simply 
decanting  an  aliquot  part  of  the  somewhat  turbid  liquid  and  titrating 
directly  in  the  presence  of  the  nitrates.  In  this  case  the  permanganate 
should  be  standardized  on  a  steel  of  similar  kind  in  which  the  manganese 
has  been  determined  gravimetrically.  High  carbon  steel  should  be 
evaporated  to  dryness  with  HNOs  and  baked. 

REFERENCES: 

STONE,  J.  Am.  Chem.  Soc.,  1896,  p.  228. 
AUCHY,  J.  Am.  Chem.  Soc.,  1896,  p.  498. 
J.  Ind.  Eng.  Chem.,  I,  p.  607. 
ORTHEY,  Z.  anal  Chem.,  XL VII,  547-560. 

Volhard's  method  as  above  given  has  the  defect  that  results  are  apt 
to  run  low.  The  reason  is  supposed  to  be  that  the  Mn02  carries  down 
with  it  some  MnO.  Fischer's  modification  of  Volhard's  method  is 
designed  to  overcome  this  difficulty.  It  is  as  follows: 

Weigh  out  1  gram  of  the  ore,  transfer  it  to  a  beaker  and  dis- 
solve in  25  c.c.  of  HC1,  sp.  gr.  1.12.  Boil  till  all  iron  is  dissolved 
and  without  cooling  add  a  1-gram  tabloid  of  KC1O3.  Drive  off 
the  free  chlorine  by  several  minutes'  boiling  and,  while  still  boil- 
ing, add  cautiously  a  little  Na2CO3.  The  violent  evolution  of 
carbon  dioxide  completes  the  removal  of  chlorine.  Transfer  to 
a  large  flask  and  dilute  to  500  c.c.,  add  NaOH  solution  till  a 


84  METALLURGICAL  ANALYSIS 

slight  precipitate  appears  which  is  dissolved  in  a  few  drops  of 
dilute  H2SO4.  Now  add  10  grams  of  ZnSO4,  heat  to  boiling  and 
add  1  gram  of  ignited  ZnO.  Titrate  with  KMnO4  with  vigorous 
shaking  and  with  the  liquid  kept  at  boiling.  When  a  perman- 
ganate color  appears,  cool  somewhat  and  add  1-2  c.c.  of  glacial 
acetic  acid  when  the  color  will  disappear.  Now  finish  the  titra- 
tion  in  the  hot  but  not  boiling  solution.  The  permanganate 
color  should  persist  after  the  solution  has  been  shaken  several 
times.  The  color  will  then  persist  for  one  to  two  hours. 

REFERENCES: 

FISCHER,  Z.  anal  Chem.,  XLVIII,  751-760. 
CAHEN  and  LITTLE,  Analyst,  XXXVI,  52-59. 

THE    BlSMUTHATE-ARSENITE    METHOD    FOR    MANGANESE 

This  method  for  manganese,  when  it  is  present  in  moderate  amounts 
(up  to  2.5  per  cent.)  is,  in  the  writer's  opinion,  the  most  accurate  known. 
No  elements  interfere  if  the  process  is  properly  carried  out.  The 
delicacy  of  the  reaction  between  manganese  and  bismuthate  in  HNO3 
is  remarkable;  as  little  as  0.00001  gram  in  50  c.c.  can  be  easily  detected. 
HC1  must  be  absent  as  it  is  ruinous  to  the  accuracy  of  the  results. 

The  method  is  based  on  the  fact  that  in  a  cold  HN03  solution  of  the 
proper  strength  manganese  is  oxidized  to  permanganic  acid  by  the 
bismuthate.  This  is  very  stable  in  cold  HNO3,  sp.  gr.  1.135,  but  in 
hot  solution  the  excess  of  bismuthate  is  decomposed  and  dissolved  and 
then  the  permanganate  is  destroyed.  In  the  cold,  however,  the  excess 
of  bismuthate  may  be  filtered  off  and  the  permanganate  titrated  by  a 
standard  reducing  agent. 

The  reactions  may  be  written: 

5Bi2O4+2Mn(N03)2+26HN03  =  10Bi(NO3)3+2HMn04-M2H20. 
2HMnO44-5Na3AsO3+4HNO3  =  5Na3AsO4+2Mn(NO3)2+3H2O. 

Process  for  Iron  and  Steel. — If  the  sample  does  not  contain 
over  1  per  cent.  Mn,  use  a  1  gram  sample;  if  1  to  2  per  cent.,  use 
a  0.5  gram  sample.  Dissolve  in  45  c.c.  water  and  15  c.c.  HNO3, 
sp.  gr.  1.42,  in  a  150  c.c.  flask.  When  dissolved  boil  until  nitrous 
fumes  are  gone.  Set  the  flask  off  the  hot  plate  and  cool  a  mo- 
ment, then  add  0.25  gram  of  " bismuthate"  and  shake  and  con- 
tinue adding  the  bismuthate  in  0.25  gram  lots  until  a  permangan- 
ate color  comes  which  persists  after  a  few  .minutes'  boiling. 
This  indicates  complete  oxidation  of  the  solution.  On  boiling, 


THE  DETERMINATION  OF  MANGANESE  85 

the  permanganic  acid  is  gradually  decomposed  to  MnO2. 
Now  add  a  few  small  crystals  of  KNO2  to  dissolve  the  MnO2 
and  boil  the  solution  several  minutes  to  expel  nitrous  fumes. 
A  little  Na2C03  added  now  will  aid  the  expulsion  of  the  fumes. 
Add  water  to  bring  the  volume  up  to  its  original  volume  and  cool 
to  tap- water  temperature.  When  cold  add  0.5  gram  of  "bis- 
muthate" and  shake  the  flask  well.  Add  20  c.c.  of  water  and 
again  shake,  then  filter  through  asbestos,  preferably  after  settling, 
and  wash  several  times  with  distilled  water. 

Titrate  the  filtrate  with  standard  arsenite  solution.  If 
the  manganese  is  high,  a  little  MnC>2  may  appear  at  the  end  but 
this  does  no  harm  as  the  titration  is  continued  until  the  brown 
MnO2  disappears.  This  only  takes  a  drop  or  two  after  the 
pink  disappears. 

Arsenite  Solution. — Add  to  0.908  gram  pure  As203  in  a  beaker, 
hot  Na2CO3  solution  until  the  As2O3  all  dissolves,  then  dilute 
to  a  liter.  One  cubic  centimeter  should  be  equal  to  0.0002  gram 
Mn.  To  standardize,  treat  a  sample  of  steel  with  known  Mn 
content  as  above  described.  Or  dissolve  0.5754  gram  KMnO4 
in  a  liter  of  water,  pipette  off  25  c.c.  and  treat  as  a  sample. 
KMnO4  has  34.76  per  cent.  Mn  so  25  c.c.  of  the  solution  contains 
0.005  gram  Mn  and  should  require  25  c.c.  of  the  arsenite  to 
titrate  it. 

Notes  on  the  Process. — It  is  necessary  to  add  the  bismuthate  to  the 
hot  HN03  solution  until  all  carbon,  sulfur,  etc.,  are  oxidized  as  well  as 
the  manganese.  Otherwise  results  will  run  low.  This  complete  oxida- 
tion is  indicated  when  the  Mn02  formed  when  the  HMn04  is  decomposed 
by  boiling,  remains  after  boiling  a  minute  or  so. 

Chromium  is  partly,  and  vanadium  completely,  oxidized  to  the  higher 
forms  H2Cr04  and  H3V04  by  the  bismuthate  in  cold  solution.  These 
do  not  harm  if  the  titration  is  carried  out  as  above  directed.  If,  how- 
ever, titration  is  carried  out  by  adding  an  excess  of  arsenite  or  other 
reducing  agent  and  then  oxidizing  back  to  standard  KMn04,  the  results 
will  be  high  if  chromium  or  vanadium  are  present  as  the  chromic  acid 
and  vanadic  acid  will  be  reduced  by  the  arsenite.  The  titration  should 
be  carried  out  by  adding  the  arsenite  until  the  permanganate  color  just 
disappears. 

The  best  material  for  filtering  off  the  Bi204  is  asbestos  and  glass  wool 
made  as  follows:  Shake  together  in  a  flask  with  water  sufficient  glass 
wool  to  fill  a  funnel  one-fourth  full  and  about  the  same  amount  of  pure 


86  METALLURGICAL  ANALYSIS 

asbestos  fiber.  Pour  into  a  funnel  and  wash  out  all  HC1.  This  filtering 
medium  does  not  easily  stop  up  and  yet  filters  perfectly.  It  may  be 
used  for  a  large  number  of  nitrations  without  changing. 

When  pig-irons  are  being  analyzed  tbiey  should  be  filtered  when  dis- 
solved in  order  to  remove  the  graphite.  In  the  analysis  of  white  irons 
it  will  be  necessary  to  treat  the  solution  several  times  with  bismuthate 
in  order  to  oxidize  the  large  amount  of  combined  carbon  present.  The 
solution  should  be  nearly  colorless  when  cold. 

Process  for  Iron  Ores. — Treat  1  gram  in  a  beaker  with  20  c.c. 
HC1  until  all  iron  is  in  solution.  Add  4  c.c.  H2SO4  and  evaporate 
until  the  H2SO4  fumes  freely,  taking  particular  care  that  all  the 
HC1  is  removed.  Cool  and  dissolve  in  45  c.c.  of  water  and  15  c.c. 
of  HN03,  filter  and  proceed  as  in  the  case  of  steels.  It  may  be 
necessary  to  examine  the  residue  for  manganese. 

For  manganese  ores  proceed  as  above  except  to  dilute  to  the 
mark  in  a  calibrated  flask,  shake  well  and  take  an  aliquot  part 
equal  to  1  per  cent,  of  manganese  on  a  1  gram  sample.  However, 
the  Volhard  process  is  more  especially  adapted  to  high  manganese 
ores. 

REFERENCES: 

BLAIR,  "Analysis  of  Iron  and  Steel,"  7th  edition,  p.  121. 
DEMOREST,  "The  Bismuthate  Method  for  Manganese,"  J.  Ind.  Eng. 

Chem.,  IV,  Jan.,  1912. 
BLUM,  J.  Am.  Chem.  Soc.,  26,  793. 

COLOR  PROCESS  FOR  MANGANESE 

When  a  solution  of  manganese  in  dilute  HNOs  is  boiled  with  Pb02 
permanganic  acid  is  formed,  coloring  the  solution  purple. 

The  depth  of  this  color  increases  with  the  amount  of  manganese 
present,  and  by  comparing  it  with  that  produced  in  the  same  way  in  a 
solution  containing  a  known  amount  of  manganese,  that  present  in  the 
first  solution  can  be  estimated.  The  method  is  sufficiently  accurate  for 
technical  purposes,  and  can  be  applied  to  steels,  pig-irons,  and  ores,  in 
which  the  per  cent,  of  manganese  is  small. 

A  standard  is  required  containing  a  known  amount  of  manganese. 
This  standard  should  be  of  precisely  the  same  kind  of  material  as  that 
to  be  analyzed;  steel  being  used  for  steel,  iron  for  iron,  ore  for  ore,  etc. 

The  Pb02  must  be  free  from  manganese.  It  must  be  light  brown  in 
color,  not  dark  brown  as  the  dark  variety  gives  low  results. 


THE  DETERMINATION  OF  MANGANESE  87 

While  the  method  is  most  commonly  applied  to  steel,  it  is  applicable 
with  slight  modifications  to  the  other  materials  mentioned. 

As  the  depth  and  shade  of  color  produced  is  influenced  by  the  time 
of  heating,  the  strength  of  the  acid,  and  the  volume  of  the  liquid,  it  is 
essential  that  the  standard  and  the  sample  be  treated  in  exactly  the 
same  manner,  and  that  the  standard  be  near  the  sample  in  percentage 
of  manganese.  The  process  can  be  conducted  in  test-tubes  or  in  small 
flasks.  The  boiling  should  be  gentle  but  continuous,  and  so  regulated 
as  to  cause  equal  concentration  of  the  liquid  in  standard  and  sample. 

Process  for  Steel. — Weigh  0.2  gram  of  the  steel  in  a  50  c.c. 
Erlenmeyer  flask.  Add  15  c.c.  of  HNOs,  sp.  gr.  1.2.  Close  the 
mouth  of  the  flask  with  a  small  glass  bulb;  heat  carefully  on  a 
hot  plate  or  steam-bath  until  the  iron  is  all  dissolved.  Transfer 
to  a  100  c.c.  graduated  flask,  filtering,  if  necessary,  and  dilute 
to  100  c.c.  Mix  thoroughly.  Now  put  10  c.c.  of  the  solution 
into  a  small  flask,  add  3  c.c.  of  HNO3,  sp.  gr.  1.2,  and  heat  care- 
fully on  a  hot  plate.  As  soon  as  the  solution  is  hot,  but  before  it 
begins  to  boil,  drop  in  a  very  little  PbO2,  and  when  the  solution 
begins  to  boil,  add  0.5  gram  more  PbO2.  Close  the  flask  with  the 
bulb  and  keep  the  solution  boiling  gently  but  continuously  for 
exactly  five  minutes.  Now  set  the  flask  in  cold  water  until  the 
PbO2  settles  to  the  bottom  and  the  violet  liquid  is  absolutely 
clear.  Avoid  exposure  to  bright  light  which  may  cause  the  color 
to  change.  A  solution  of  the  standard  steel  should  be  prepared 
and  treated  in  the  same  way  and  at  the  same  time. 

Pour  off  the  two  solutions  into  two  graduated  tubes  and  dilute 
the  darker  till  the  colors  match  when  compared  over  a  sheet  of 
white  paper.  The  volumes  will  then  have  the  same  ratio  as  the 
amount  of  manganese  in  the  standard  and  test  sample. 

Small  flasks  used  in  this  way  and  kept  closed  with  glass  bulbs 
are  as  satisfactory  as  the  special  calcium  chloride  bath  and  test- 
tubes  sometimes  used.  The  heavy  lead  precipitate  settles  so 
completely  to  the  bottom  that  with  care  the  liquid  can  nearly 
all  be  poured  off  without  disturbing  it.  Where  the  standard  and 
the  sample  are  close  in  manganese  content,  the  small  amount  of 
liquid  left  in  each  flask  will  not  appreciably  affect  the  results  if 
the  original  volumes  were  about  equal.  Eight-inch  test-tubes 
may  be  used  instead  of  the  flasks.  They  can  be  heated  in  a 
calcium  chloride  bath  at  115°C..  or  on  a  sand-bath  provided  with 
a  wire  rack  for  holding  the  tubes. 


&8  METALLURGICAL  ANALYSIS 

The  PbO2  settles  a  little  better  in  the  tubes,  which  should  be 
placed  upright  in  cold  water.  If  a  centrifugal  machine  is  avail- 
able (such  for  instance  as  is  used  for  separating  the  phosphorus 
precipitate  for  measuring  in  the  Goetz  process),  the  PbO2  can 
be  rapidly  separated  by  pouring  the  contents  of  the  flasks  into 
test-tubes  and  whirling  them  in  the  machine. 

The  addition  of  a  little  PbC>2  before  the  boiling  commences 
causes  this  to  start  off  quietly,  and  on  adding  the  rest  of  the 
reagent  there  is  no  violent  action  such  as  is  likely  to  take  place 
if  the  oxide  is  added  at  once  to  the  boiling  liquid  and  which  may 
throw  liquid  out  of  the  flask. 

When  the  manganese  is  very  low,  25  c.c.  or  more  of  the  solution 
of  the  steel  may  be  used  instead  of  the  10  c.c.  directed,  provided 
the  amount  of  HNOs  is  proportionately  increased. 

Dilution  and  division  of  the  solution  as  directed  is  desirable, 
where  the  amount  of  manganese  is  sufficient  to  give  a  deep  color. 
It  is  unnecessary  in  low  manganese  steel.  In  this  case  proceed 
as  follows: 

Dissolve  0.2  gram  of  the  steel  in  15  c.c.  HNO3,  1.2  sp.  gr.  Boil 
till  nitrous  fumes  are  expelled  and  add  15  c.c.  of  water,  then  add 
the  PbC>2  and  boil  as  before  directed.  Allow  to  settle,  decant  off, 
cool,  and  compare.  Use  care  to  heat  the  standard  and  sample 
equally,  both  during  the  solution  and  after  adding  the  PbO2. 
Instead  of  dissolving  the  standard  each  time  a  test  is  made,  a 
quantity  may  be  dissolved  and  the  solution  then  diluted  so  that 
10  c.c.  corresponds  to  the  weight  of  the  sample  taken  in  the  test. 
This  volume  may  then  be  taken  for  comparison  with  each  set  of 
tests.  Thus  for  the  first  process  where  the  solution  is  diluted 
and  divided,  dissolve  2  grams  of  the  standard  steel,  dilute  to  1 
liter  and  use  10  c.c.  each  time  for  comparison. 

For  steels  of  moderate  percentage  of  manganese  the  time  of 
boiling  may  be  shortened  to  three  minutes. 

Process  for  Pig-iron. — Dissolve  0.2  gram  in  10  c.c.  HN03, 
sp.  gr.  1.2.  Add  %  c.c.  HC1  and  boil  down  to  1  or  2  c.c.  Add 
10  c.c.  concentrated  HNO3  and  boil  down  one-half.  Now  dilute 
to  100  c.c.,  filter  through  a  dry  filter,  take  an  aliquot  part  of  the 
filtrate  and  proceed  as  in  the  regular  process.  Use  a  pig-iron 
standard.  With  very  low  manganese  or  coarse-grained  iron  it 
may  be  desirable  to  take  larger  amounts  to  secure  an  average. 


THE  DETERMINATION  OF  MANGANESE  80 

In  this  case  use  1  gram  and  dilute  to  100  or  500  c.c.  according  to 
the  amount  of  manganese  present. 

Process  for  Ores. — Dissolve  0.2  gram  in  5  c.c.  of  HC1.  Boil 
down  to  a  syrup;  add  10  c.c.  of  concentrated  HN03,  evaporate 
again  to  a  syrup.  Add  10  c.c.  of  HNO3,  1.2  sp.  gr.,  dilute,  filter 
and  proceed  as  with  pig-iron,  using  an  ore  standard. 

REFERENCES: 

HUNT,  Trans.  Am.  Inst.  Mining  Eng.,  XV,  p.  164. 

LEAD  PEROXIDE-ARSENITE  METHOD 

Instead  of  determining  the  manganese  by  comparing  the  colors  in  the 
above  method,  the  permanganate  may  be  titrated  by  a  standard  reduc- 
ing agent,  preferably  arsenite  because  of  its  keeping  qualities.  The 
writer  prefers  to  use  bismuthate  rather  than  PbOs  because  of  its  more 
certain  oxidizing  power,  but  the  Pb02  is  cheaper. 

Process. — Proceed  exactly  as  directed  above  but  instead  of 
decanting  from  the  lead  peroxide,  filter  and  wash  twice.  Now 
titrate  with  the  arsenite  as  directed  in  the  bismuthate-arsenite 
process. 

COLOR  METHOD  USING  AMMONIUM  PERSULFATE 

This  method  is  due  to  Marshal  and  Walters.  It  depends  upon  the 
fact  that  if  ammonium  persulfate  (NH^SOO  is  added  to  a  solution  of 
manganese  in  dilute  nitric  or  sulfuric  acid,  it  will,  on  warming,  promptly 
and  completely  oxidize  the  manganese  to  permanganic  acid,  provided  a 
small  amount  of  silver  nitrate  is  present.  The  silver  salt  is  essential,  for 
if  not  present  the  manganese  will  be  precipitated  as  Mn02.  If  too  much 
silver  salt  is  present,  silver  peroxide  will  precipitate  and  make  the  solu- 
tion muddy. 

The  solution  should  not  be  boiled,  but  merely  warmed  until  the  color 
develops. 

It  is  said  that  the  persulfate  should  be  slightly  damp,  but  we  have 
used  this  salt  dried  in  a  desiccator  with  satisfactory  results. 

Walter's  Process  for  Steel.— Dissolve  0.1  or  0.2  gram  of  the 
steel,  according  to  the  percentage  of  manganese,  in  10  c.c.  of 
HNO3,  sp.  gr.  1.2.  Heat  until  all  nitrous  fumes  are  driven  off. 
Now  add  15  c.c.  of  a  solution  of  silver  nitrate  containing  1.33 
gram  of  the  salt  to  1  liter  of  water.  This  will  cool  the  solution 
considerably.  Now  immediately  add  about  1  gram  of  ammonium 


90  METALLURGICAL  ANALYSIS 

persulfate,  and  warm  until  the  color  commences  to  develop,  and 
then  for  about  a  half  minute  longer.  Remove  from  the  heat  and 
set  it  in  cold  water  while  the  evolution  of  oxygen  continues.  As 
soon  as  the  solution  is  cool,  compare  it  with  a  solution  of  standard 
steel  treated  in  the  same  manner. 

The  solution  of  the  standard  steel  may  be  prepared  in  quantity, 
as  noted  before,  by  dissolving  several  grams  of  the  metal  in  a 
sufficient  amount  of  nitric  acid,  sp.  gr.  1.2,  and  diluting  with  the 
same  strength  acid  until  10  c.c.  of  the  solution  contain  0.2  gram 
of  steel.  Ten  cubic  centimeters  of  this  solution  are  then  used 
with  each  set  of  determinations. 

REFERENCE: 

Chemical  News,  Feb.  15  and  Nov.  15,  1911. 


CHAPTER  VII 
THE  DETERMINATION  OF  SULFUR 

Sulfur  occurs  in  iron  ores  as  sulfides,  such  as  pyrite  (FeS2)  and 
sphalerite  (ZnS)  and  also  as  sulfates,  such  as  gypsum  (CaS04,  2H20), 
barite  (BaS04)  and  celestite  (SrS04).  In  iron  and  steel  it  occurs  as 
sulfide  only.  In  the  gravimetric  methods  for  determining  sulfur  it  is 
first  converted  into  some  soluble  sulfate  and  then  the  sulfuric  acid 
precipitated  by  barium  chloride  and  weighed  as  barium  sulfate. 

DIRECT  OXIDATION  METHODS 

Conversion  of  the  Sulfides  to  Sulfates. — All  sulfides  are  completely 
oxidized  to  sulfates  when  fused  with  a  mixture  of  dry  Na2C03  and 
NaN03  or  with  Na202. 

As  free  sulfur  and  certain  disulfides  give  off  sulfur  vapor  at  a  com- 
paratively low  temperature  (below  the  fusing-point  of  Na2C03),  when 
these  are  present  care  must  be  taken  to  prevent  loss  by  the  escape  of  this 
vapor.  The  mixture  of  ore  and  flux  must  be  covered  with  a  layer  of  the 
pure  "fusion  mixture"  and  heated  carefully. 

After  fusion  all  the  sulfur,  whether  originally  present  as  sulfide  or 
sulfate  (even  in  BaS04)  will  be  found  as  Na2S04,  the  bases  present 
remaining  as  oxides  or  carbonates.  When  the  fused  mass  is  boiled  with 
water  till  thoroughly  disintegrated  and  then  filtered  off  and  washed,  the 
sulfate  all  passes  into  the  filtrate. 

Sulfides  can  be  more  or  less  completely  oxidized  to  sulfates  in  the 
"wet  way"  by  treating  them  with  hot  concentrated  HN03  or  aqua 
regia.  Wet  methods  are  not  very  satisfactory,  as  free  sulfur  is  liable  to 
separate  and  fuse  to  globules,  its  melting-point  being  below  the  boil- 
ing-point of  HNO3.  Once  in  this  form  it  is  very  slowly  oxidized  by 
boiling  with  ordinary  oxidizing  agents.  Iron  sulfide  can  be  completely 
oxidized,  however,  by  heating  with  a  large  excess  of  concentrated 
HNO3  and  adding  a  little  powdered  KC103. 

When  iron  sulfide,  or  even  iron  containing  but  little  sulfur,  is  dissolved 
in  dilute  HN03,  1.2  sp.  gr.,  a  considerable  proportion  of  the  sulfur 
separates  as  such  and  escapes  oxidation. 

Solutions  containing  ferric  sulfate,  on  evaporation  to  dryness  and 

91 


92  METALLURGICAL  ANALYH1H 

"  baking,"  as  is  common  in  iron  analysis,  may  lose  S03  unless  enough 
potassium  or  sodium  is  added  to  hold  it  all  in  combination  with  the 
alkali,  as  the  sulfate  of  iron  is  easily  decomposed  by  heat  and  S03 
expelled. 

REFERENCES: 

See  FRESENIUS,    "Quantitative  Analysis;"  also   PHILLIPS,   J.   Am. 
Chem.  Soc.,  1896,  p.  1079. 

THE  PRECIPITATION  OF  THE  SO3  BY  BaCl2 

This  precipitation  must  be  conducted  under  carefully  regulated  con- 
ditions, if  the  results  are  to  be  satisfactory. 

When  the  amount  of  sulfur  present  is  very  small  the  contamination  of 
the  BaS(>4  is  not  apt  to  be  important  and  the  chief  thing  is  to  get  the 
sulfur  completely  precipitated;  but  when  large  amounts  of  sulfur  are 
to  be  precipitated,  as  when  pyrite  is  to  be  analyzed,  the  case  is  very 
different  and  great  care  must  be  taken  to  have  the  BaS04  pure  as  well 
as  completely  precipitated. 

When  alkalies  are  present,  all  BaS04  precipitates  carry  down  alkali 
sulfates,  the  error  being  worst  if  alkali  chlorides  are  present.  If  ammo- 
nium salts  are  present,  ammonium  sulfate  is  carried  down,  and  is  of 
course  lost  on  ignition.  In  the  presence  of  much  alkali  chloride,  the 
precipitate  contains  a  certain  amount  of  free  sulfuric  acid.  All  of  these 
errors  make  results  run  low,  in  some  cases  perhaps  as  much  as  several 
per  cent,  of  the  total  weight. 

In  addition  to  these  minus  errors,  there  are  plus  errors.  All  barium 
sulfate  precipitates  contain  barium  chloride.  If  the  precipitation  is 
made  very  slowly,  the  amount  of  this  is  very  small.  When  the  precipi- 
tation is  made  rapidly,  it  is  much  larger.  Nitrates  are  occluded  by 
barium  sulfate,  giving  results  which  are  high.  When  barium  sulfate  is 
precipitated  from  solutions  containing  much  ferric  iron,  iron  salts  will 
adhere  to  the  precipitate,  making  it  reddish  in  color,  unless  considerable 
HC1  is  present.  Some  of  the  sulfuric  acid  appears  to  be  in  combination 
with  the  iron  instead  of  with  the  barium,  and  is  driven  off  on  ignition, 
causing  low  results.  Water  alone  will  not  wash  out  any  of  the  above 
salts  occluded  with  the  barium  sulfate. 

Barium  sulfate  while  very  insoluble  in  water  is  not  so  in  dilute  acids, 
the  amount  dissolved  increasing  with  the  concentration  of  the  acid, 
though  the  presence  of  a  considerable  excess  of  BaCl2  very  largely 
decreases  the  solubility  of  the  barium  sulfate  in  HC1.  Acid  solutions 
of  FeCl3,  when  hot,  hold  a  little  BaSO4  in  solution,  which  separates 
when  the  liquid  cools. 

The  precipitate  of  BaS04  is  fine,  liable  to  run  through  the  filter  paper, 


THE  DETERMINATION  OF  SULFUR  93 

if  precipitated  cold,  and  so  should  be  precipitated  hot  and  allowed  to 
stand  on  a  warm  plate  with  frequent  stirring.  In  this  way  the  precipi- 
tate will  grow  dense  and  granular  so  that  it  can  be  easily  filtered. 

It  will  be  seen  from  the  above  that  the  determination  of  sulfur  when 
present  in  large  amounts  is  attended  with  many  difficulties  and  for 
accurate  results  correction  must  be  made  by  analysis  of  the  precipitate. 
For  good  technical  results  perhaps  the  best  way  is  to  wash  the  precipi- 
tate off  the  filter  back  into  the  beaker,  add  HC1  equal  to  the  water 
present  and  evaporate  almost  to  dryness,  add  100  c.c.  of  water  and 
5  c.c.  of  10  per  cent.  BaCl2,  let  settle  and  filter. 

REFERENCES: 

HILLEBRAND,  Bulletin  422,  U.  S.  Geol.  Survey,  p.  195. 

ALLEN  and  JOHNSON,  J.  Am.  Chem.  Soc.,  May,  1910,  p.  588. 

ARCHBUTT,  J.  Soc.  Chem.  Ind.,  IX,  p.  25. 

LUNGE,  J.  Soc.  Chem.  Ind.,  VIII,  pp.  967  and  819. 

AUCHY,  J.  Am.  Chem.  Soc.,  1901,  p.  147;  Am.  Chem.  J.,  1902,  p.  495. 

Process  for  Sulfur  in  Iron  Ores. — Mix  1  gram  of  the  finely 
pulverized  ore  with  5  grams  of  dry  Na2CO3  and  0.5  to  1  gram 
of  NaNO3,  according  to  the  amount  of  sulfur  in  the  ore.  Put 
the  mixture  in  a  platinum  crucible  and  fuse  carefully.  As  soon 
as  it  is  well  melted,  chill  the  crucible  by  dipping  the  bottom  into 
water.  This  will  usually  loosen  the  cake  so  that  it  can  be  re- 
moved from  the  crucible. 

As  ordinary  gas  contains  sulfur,  fusions  made  over  it  are  likely 
to  absorb  some  SO 2  from  the  flame.  Therefore  an  alcohol  or 
gasoline  blast  lamp  should  be  used.  If  gas  is  used,  the  crucible 
must  be  kept  covered  during  the  fusion  and  should  be  protected 
by  inserting  it  into  a  tightly  fitting  collar  of  sheet  asbestos 
nearly  to  the  top.  This  will  act  as  a  shield  to  prevent  the  prod- 
ucts of  combustion  from  getting  into  the  crucible.  In  accurate 
work  it  is  always  necessary  to  make  a  blank  analysis  and  deter- 
mine the  small  amount  of  sulfur  contained  in  the  reagents  or 
absorbed  from  the  gas  flames.  Deduct  this  from  the  amount 
found  when  working  on  the  ore. 

Boil  out  the  fusion  with  water  until  all  the  material  is  soft  and 
no  hard  lumps  remain.  If  the  solution  is  colored  by  Na2MnO4, 
add  a  few  drops  of  alcohol.  Filter  and  wash  well  with  hot  water. 
Add  HC1  to  the  cold  solution  which  should  have  a  volume  of 
about  100  c.c.  The  acid  should  be  added  until  the  solution  is 
just  acid,  then  about  4  c.c.  more,  Now  heat  nearly  to  boiling 


94  METALLURGICAL  ANALYSIS 

and  add  5  to  10  c.c.  of  a  10  per  cent,  solution  of  BaCl2  previously 
diluted  with  10  to  20  c.c.  of  water  and  heated.  Stir  and  let  the 
precipitate  of  BaSO4  settle.  When  clear,  filter,  wash  with  hot 
water,  ignite  and  weigh  the  BaS04.  This  weight  multiplied 
by  0.1374  gives  the  amount  of  S. 

If  it  is  suspected  that  the  BaS04  is  contaminated  with  SiO2 
it  should  be  treated  with  HF.  It  is  a  good  thing  to  do  in  any 
case.  Add  to  the  ignited  precipitate  a  drop  of  H2SC>4  and  2  c.c. 
of  HF.  Evaporate  off  the  acids  and  finally  again  ignite  and 
weigh. 

Notes  on  the  Process. — BaS04  is  easily  reduced  to  BaS  by  heating 
with  carbon.  This  may  occur  in  the  crucible  and  will  make  the  results 
come  low;  hence,  in  igniting  the  precipitate  detach  it  as  far  as  possible 
from  the  filter,  burn  the  paper  carefully  on  a  platinum  wire,  avoiding  a 
high  heat.  Add  the  ash  to  the  precipitate  in  the  crucible  and  heat  gently 
with  the  cover  off  until  all  the  carbon  is  burned,  finally  igniting  to  a 
bright  red  heat. 

Instead  of  drying  the  paper,  the  wet  filter  and  precipitate  may  be  ig- 
nited together  by  proceeding  as  follows :  Put  the  filter  paper  containing 
the  precipitate  into  a  good-sized  platinum  crucible.  The  paper  should 
be  put  in  point  down  and  open,  just  as  it  sets  in  the  funnel.  Now 
set  the  uncovered  crucible  over  a  very  low  flame  and  dry  out  the  paper 
carefully.  Then  continue  the  heating  to  char  the  paper  without 
letting  it  ignite.  Should  it  catch  fire,  extinguish  the  flame  by  momen- 
tarily covering  the  crucible.  When  all  the  volatile  matter  is  expelled, 
slightly  increase  the  heat  which  should  not,  however,  exceed  a  dull  red. 
The  carbon  will  now  all  burn  away  and  the  precipitate  become  white. 
Finally  raise  the  temperature  to  bright  redness.  Cool  and  weigh  as 
before.  This  process  is  called  " smoking  off"  the  filter  and  saves  much 
time.  It  can  be  used  safely  on  all  small  BaS04  precipitates.  After 
weighing  the  precipitate,  add  a  little  water  to  it  and  test  with  turmeric 
paper.  If  it  reacts  alkaline,  the  results  are  untrustworthy,  as  reduction 
has  occurred;  in  this  case  add  a  drop  of  H2S04;  heat  till  dry,  ignite  and 
weigh  again,  taking  the  second  weight  as  the  correct  one. 

WET  OXIDATION  METHOD  FOR  SULFUR  IN  ORES 

This  method  fails  to  determine  the  sulfur  in  any  BaS04  or  PbS04 
contained  in  the  ore.  Therefore  it  is  not  so  generally  applicable  as  the 
fusion  method  unless  the  residue  is  separately  treated  by  the  fusion 
method  and  any  sulfur  thus  obtained  added  to  that  obtained  by  the  wet 
method. 


THE  DETERMINATION  OF  KVLFVR  95 

Process  of  Analyses. — Weigh  1  to  5  grams  of  the  very  finely 
pulverized  ore.  Put  it  in  a  covered  casserole  or  beaker  and  add 
20  c.c.  of  concentrated  HNO3.  Heat  and  add  1  gram  of  KC1O3 
in  several  portions.  Now  digest  at  a  moderate  heat  till  all  action 
ceases,  then  evaporate  off  most  of  the  HNO3.  Add  an  excess  of 
HC1  and  warm  until  the  iron  is  all  dissolved.  Evaporate  to 
dryness  and  proceed  as  with  the  dried  residue  in  the  determination 
of  sulfur  in  iron  or  steel. 

When  sulfur  is  present  in  large  amounts,  as  for  instance,  in 
pyrite,  it  is  necessary  that  the  BaS(>4  be  precipitated  from  a  solu- 
tion free  from  iron.  Dissolve  0.5  gram  of  the  very  finely  ground 
sample  in  20  c.c.  of  aqua  regia  in  a  beaker  with  a  watch-glass 
cover.  Heat  until  decomposition  is  complete,  then  evaporate 
to  dryness.  If  necessary  use  a  little  KC103  with  the  aqua  regia 
to  dissolve  the  pyrite.  Moisten  the  dry  mass  with  1  c.c.  HC1 
and  100  c.c.  of  water.  Heat  until  all  except  the  gangue  is  dis- 
solved and  filter.  To  the  cold  solution  add  ammonia  until 
alkaline,  heat  to  boiling  and  filter  off  the  Fe(OH)3  and  wash 
thoroughly.  Make  the  filtrate  acid  with  HC1,  heat  to  boiling 
and  add  slowly  BaCl2  with  constant  stirring.  After  standing 
some  time,  filter  and  wash,  transfer  the  BaSO4back  to  the  beaker, 
add  as  much  HC1  as  there  is  water  present,  evaporate  almost  to 
dryness,  add  100  c.c.  water  and  then  20  c.c.  BaCl2,  allow  to  stand 
a  half  hour,  filter  and  wash.  Ignite  very  carefully  to  prevent 
reduction  of  the  BaS04. 

METHOD  FOR  SULFUR  IN  IRON  AND  STEEL 

As  the  sulfur  is  usually  present  in  these  metals  in  very  small  percent- 
ages only,  its  accurate  determination  demands  great  care. 

Process  of  Analysis. — Take  from  2  to  5  grams  according  to  the 
percentage  of  sulfur.  Add  25  to  40  c.c.  concentrated  HN03. 
Cool  the  dish  if  the  action  is  too  rapid,  or  heat  it  if  it  is  too  slow. 
The  rate  of  solution  must  not  be  too  rapid  or  low  results  may 
follow. 

When  the  metal  is  nearly  all  dissolved,  heat  to  boiling  and  add 
2  to  3  c.c.  of  concentrated  HC1  to  complete  the  solution.  Now 
add  about  0.5  gram  KC103  free  from  sulfur.  Boil  to  dryness 
and  bake  on  a  hot  plate  10  minutes.  Add  10  to  20  c.c.  con- 


96  METALLURGICAL  ANALYSIS 

centrated  HC1  to  dissolve  the  residue  and  again  dry  down 
thoroughly.  Dissolve  again  in  15  to  40  c.c.  of  concentrated 
HC1.  Evaporate  the  solution  until  a  skin  begins  to  form  on 
the  surface  or  until  it  becomes  syrupy.  Now  add  5  to  10  c.c. 
of  concentrated  HC1,  according  to  the  amount  of  iron  taken. 
When  all  the  iron  dissolves  dilute  the  liquid  with  its  own  volume 
of  hot  water  and  filter  into  a  small  beaker  through  a  paper  pre- 
viously washed  out  with  a  little  hot  dilute  HC1  (this  facilitates 
filtration).  Wash  the  dish  and  insoluble  residue  with  hot  water. 

The  filtrate  and  washings  must  not  exceed  75  c.c.  Now  warm 
to  about  60°C.  and  add  10  c.c.  of  a  10  per  cent,  solution  of  BaC^. 
Let  stand  till  the  precipitate  settles,  leaving  the  liquid  perfectly 
clear.  (Two  hours  is  sufficient  if  everything  is  right.) 

Filter  onto  a  small  ashless  filter,  wash  with  water  containing  a 
few  drops  of  HC1,  ignite  and  weigh  the  BaS04.  Test  the  filtrate 
by  the  addition  of  considerably  more  BaCl2  solution  which  must 
give  no  additional  precipitate. 

The  residue  from  which  the  solution  for  the  determination  of 
sulfur  is  filtered  must  contain  no  basic  iron  salts,  as  these  may 
hold  sulfur.  .  These  are  likely  to  form  if  the  HC1  solution  is  con- 
centrated too  far  and  insufficient  acid  is  added  before  dilution. 

REFERENCE: 

J.  Anal,  and  App.  Chem.,  VI,  p.  318. 

Notes  on  the  Process. — It  is  imperatively  necessary  that  a  blank  be 
run  on  all  the  reagents  used  in  the  process  and  the  weight  of  a  BaS04 
obtained  in  this  way  deducted  from  that  found  in  the  analysis. 

Certain  high  carbon  steels  and  most  ferro-silicons  will  resist  the  action 
of  concentrated  HN03  almost  entirely.  When  treating  such  metals  add 
some  potassium  chlorate  with  the  nitric  acid  at  the  start,  and  also  at 
intervals  add  concentrated  HC1,  1  c.c.  at  a  time,  until  the  metal  is 
dissolved;  then  add  more  KC103  and  proceed  as  usual. 

Ferro-silicons  with  over  10  per  cent,  of  silicon  will  resist  the  action  of 
all  the  ordinary  solvents.  These  and  other  insoluble  alloys  cannot  be 
treated  by  wet  methods  for  the  determination  of  sulfur. 

Where  the  percentage  of  silicon  does  not  exceed  about  15  per  cent.,  the 
small  addition  of  sodium  fluoride  to  the  HN03  as  described  under  Phos- 
phorus on  page  46,  will  usually  bring  the  metal  into  solution  and  the  de- 
termination can  then  be  carried  out  as  usual,  by  adding  the  chlorate, 
evaporating,  baking  and  taking  up  in  HC1.  In  other  cases  the  metal 
must  be  fused.  The  fusion  is  best  made  in  a  platinum  crucible  with  a 


THE  DETERMINATION  OF  MILFUR  97 

mixture  of  equal  parts  of  NaN03  and  Na2C03  using  at  least  six  parts 
of  the  mixture  to  one  of  the  metal.  The  fusion  can  be  then  soaked 
out  with  water  and  the  water  solution  treated  as  in  the  case  of  an  ore. 
The  sulfur  will  all  go  into  the  water  solution,  provided  the  iron  is 
completely  oxidized.  It  is  essential  that  the  metal  be  very  finely  pow- 
dered. The  peroxide  of  sodium  can  be  substituted  for  the  nitrate  or  may 
be  used  alone,  in  which  case  at  least  8  grams  of  the  reagent  must  be 
used  for  one  of  metal,  and  the  fusion  made  in  a  nickel  crucible.  Blanks 
must  be  run  on  all  the  reagents. 

REFERENCES: 

F.  C.  PHILLIPS,  J.  Am.  Chem.  Soc.,  1896,  p.  1079. 
E.  H.  SANITER,  J.  Soc.  Chem.  Ind.,  1896,  p.  155. 

THE  DETERMINATION  OF  SULFUR  IN  PIG-IRON  AND  STEEL  BY 
EVOLUTION  AS  H2S 

The  direct  oxidation  methods  are  accurate  and  the  only  ones  that  can 
be  relied  upon  to  give  with  certainty  the  total  sulfur  in  any  material. 
But  they  are  too  slow  to  answer  for  control  work.  For  such  purposes 
the  evolution  methods  are  very  generally  used.  They  are  either  gravi- 
metric or  volumetric  and  can  be  made  extremely  rapid.  For  some 
materials  they  will  give  reliable  results. 

These  methods  all  depend  upon  the  assumption  that  when  iron  is 
dissolved  in  HC1  the  whole  of  the  S  is  evolved  as  H2S  and  passes  off 
with  the  excess  of  hydrogen.  This  is  probably  true  or  nearly  so  for  steel 
containing  but  little  carbon  and  possibly  for  gray  pig-iron;  it  certainly 
is  not  true  for  white  iron  and  mottled  irons  high  in  combined  carbon; 
and  probably  not  true  for  high-carbon  steels  and  some  ferro-silicons, 
especially  those  containing  much  sulfur. 

In  these  latter  materials  part  of  the  sulfur  appears  to  be  evolved  as 
more  or  less  volatile  liquid  or  possibly  gaseous  compounds  of  carbon, 
hydrogen  and  sulfur  and  not  as  H2S.  The  proportion  of  the  sulfur 
evolved  as  H2S  will  vary  in  the  same  iron  if  the  heat  treatment  has  been 
different;  if  slowly  cooled,  it  may  be  gray  and  evolve  most  of  the  sulfur 
as  H2S;  if  suddenly  cooled  by  chilling  in  water  (shot  samples)  it  will  be 
white  and  only  a  small  portion  of  its  sulfur  may  be  evolved  as  H2S. 
Hence  by  evolution  methods  the  latter  sample  would  show  a  much  lower 
percentage  of  sulfur  than  the  former.  The  sulfur  that  is  lost  is  in  the 
form  of  (CH3)2S  or  some  similar  form.  The  higher  the  percentage  of 
carbon  in  solid  solution  (Martensite)  in  the  iron  the  more  sulfur  is  thus 
lost.  Part  of  this  goes  over  with  the  gases  and  part  stays  behind  in  the 
flask.  If  the  evolved  gases  be  passed  with  hydrogen  through  a  glass 

7 


98  METALLURGICAL  ANALYSIS 

tube  heated  to  dull  redness  the  sulfur  compounds  are  changed  to  H2S. 
If  the  tube  is  filled  with  asbestos  coated  with  platinum  black  the  action 
is  more  rapid.  Care  must  be  taken  to  exclude  air  or  explosion  will  result. 
The  amount  of  sulfur  evolved  in  combination  as  (CH3)2S  increases  with 
the  manganese  in  the  sample  and  decreases  with  the  phosphorus.  Of 
that  retained  in  the  flask,  part  may  be  in  this  form  and  if  any  titanium 
is  present  some  will  be  held  in  combination  with  the  titanium.  Phillips 
has  shown  that  sulfur  retained  in  the  flask  as  difficultly  volatile  organic 
compounds  may  be  distilled  off  by  prolonged  boiling. 

By  taking  certain  precautions  the  amount  of  sulfur  lost  can  be  re- 
duced to  a  very  small  amount  and  the  results  by  the  evolution  process 
can  be  made  to  check  fairly  well  with  the  standard  process  even  on  pig- 
irons.  These  precautions  are  as  follows: 

(1)  The  weighed  sample  should  be  annealed  in  a  non-oxidizing 
atmosphere  according  to  a  certain  procedure.  This  changes  the  marten- 
site  to  pearlite  with  cementite,  graphite  or  ferrite  according  to  the 
amount  of  carbon.  (2)  The  speed  of  solution  should  be  as  great  as 
possible.  (3)  The  acid  used  should  be  concentrated  acid,  of  sp.  gr. 
1.19.  Under  these  conditions  the  use  of  a  hot  tube  through  which  to 
pass  the  evolved  gases  is  not  necessary. 

Ordinary  low-carbon  steels  do  not  have  to  be  annealed,  but  high- 
carbon  steels,  pig-irons  and  the  alloy  steels,  such  as  self-hardening  steels 
and  nickel-chromium  steels  must  be  annealed  to  get  correct  results. 

For  rapid  work,  as  for  furnace  control,  the  annealing  of  the  sample  may 
be  omitted  but  it  should  be  understood  that  this  always  gives  low  results, 
sometimes  as  much  as  20  per  cent,  low,  when  the  sample  is  a  pig-iron. 

On  the  other  hand,  in  the  case  of  steels,  the  results  for  sulfur  by  the 
evolution  process  may  give  too  high  results.  Besides  H2S  other  gases 
are  given  off  which  may  affect  the  results.  These  are  hydrocarbons  and 
PH3  and  AsH3  which  are  absorbed  to  a  certain  extent  and  affect  iodine 
used  for  titrating,  but  do  not  affect  gravimetric  results.  According  to 
Elliot  these  are  not  absorbed  in  CdCl2  solution  containing  acetic  acid 
and  ammonium  acetate  as  they  are  in  alkaline  solutions  or  in  solutions 
of  lead,  zinc,  or  copper. 

The  H2S  evolved  is  very  easily  decomposed  by  comparatively  feeble 
oxidizing  agents,  water  being  formed  and  free  sulfur  deposited.  Pro- 
longed contact  with  air  and  sunlight,  the  presence  of  FeCl3,  traces  of 
chlorine,  all  act  on  it  in  this  way,  and  must  be  avoided  in  the  process. 
There  is  no  necessity,  however,  of  working  in  an  atmosphere  of  hydrogen 
or  of  carbon  dioxide  if  the  process  is  rapidly  conducted.  On  the  other 
hand,  slow  evolution,  or  the  use  of  HC1  containing  traces  of  chlorine  or 
FeCl3  will  cause  decomposition  of  the  H2S  and  retention  of  sulfur  in  the 
residue. 


THE  DETERMINATION  OF  SULFUR  99 

Rusting  of 'the  drillings  previous  to  the  addition  of  HC1  leads  to  the 
formation  of  FeCl3  and  may  cause  a  separation  of  sulfur  from  the  gas 
in  the  flask.  Dilute  HC1  (1  : 1)  is  usually  used  in  these  methods  but 
according  to  the  writer's  experience  this  sometimes  fails  to  cause  com- 
plete evolution  of  the  sulfur  as  H2S  where  the  concentrated  acid  succeeds. 
(See  PHILLIPS,  J.  Am.  Chem.  Soc.,  1895,  p.  891.) 

While  the  H2S  is  easily  absorbed,  the  organic  sulfur  compounds  are 
only  slowly  and  incompletely  taken  up.  Long  boiling  is  frequently 
necessary  to  drive  them  completely  out  of  the  flask  in  which  the  iron 
is  dissolved.  It  is  evident  from  what  has  been  said  that  the  evolution 
processes  are  reliable  only  when  they  are  checked  by  using  the  gravi- 
metric process  on  the  same  kind  of  sample. 

The  H2S  evolved  may  be  determined  in  many  ways.  It  may  be 
absorbed  in  an  alkaline  solution  of  lead  acetate,  then  oxidized  to  80s 
and  precipitated  by  BaCl2,  or  it  may  be  absorbed  in  a  solution  of  HC1 
and  bromine  and  the  H2SO4  formed  precipitated  by  Bad 2,  or  in  an  al- 
kaline solution  of  KMn04  and  precipitated  as  before.  Some  chemists 
absorb  the  H2S  in  a  CuS04  solution,  filter  off  the  copper  sulfide,  ignite 
and  weigh  as  CuO.  The  most  widely  used  method  is,  however,  a 
volumetric  one  in  which  the  H2S  is  titrated  with  a  standard  iodine  solu- 
tion. It  is  very  rapid  and  is  quite  as  accurate  as  the  other  evolution 
methods. 

THE  IODINE  METHOD  FOR  SULFUR 

The  H2S  may  be  absorbed  in  NaOH  or  KOH  or  an  ammoniacal  solu- 
tion of  zinc  or  cadmium.  The  cadmium  solution  is  preferred  because  it 
fixes  the  sulfur  in  a  visible  form  and  is  not  easily  altered  on  standing. 
KOH  and  NaOH  are  liable  to  contain  oxidizing  impurities  such  as 
nitrites  or  ferric  hydroxide  which  would  oxidize  H2S. 

The  reactions  involved  in  the  process  are  as  follows: 

FeS(or  MnS)+2HCl  =  FeCl2(or  MnCl2)+H2S. 
H2S+CdCl2  =  CdS+2HCl. 

The  HC1  liberated  is  neutralized  by  the  NH4OH  present.  When  the 
H2S  has  all  come  over,  the  solution  is  diluted  and  strong  HC1  is  added  in 
excess;  then  the  reverse  reaction  takes  place, 

CdS+2HCl  =  H2S+CdCl2. 

A  considerable  excess  of  HC1  is  necessary  to  completely  dissolve  all 
of  the  CdS.     The  volume  of  the  solution  should  be  very  large  to  prevent 
the  escape  of  the  liberated  H2S.     Also  it  should  not  be  hot. 
The  H2S  is  then  titrated  with  iodine. 

H2S+2I  =  2HI+S. 


100  METALLURGICAL  ANALYSIS 

The  liberated  sulfur  causes  the  liquid  to  become  curiously  opales- 
cent and  show  various  colors,  but  this  does  not  at  all  obscure  the  end 
reaction  which  is  very  sharp.  Before  titration  a  little  starch  solution  is 
added  to  the  liquid  to  be  titrated.  One  drop  of  iodine  in  excess  of  the 
amount  required  to  titrate  the  EbS  causes  an  intense  blue  color  of  "  starch 
iodide"  to  be  formed. 

Preparation  of  the  Starch  Solution. — Stir  5  grams  of  starch  into 
200  c.c.  of  cold  water.  Heat  the  liquid  to  boiling  with  constant 
stirring  until  the  starch  is  thoroughly  dissolved.  Now  dilute 
the  liquid  with  cold  water  to  about  a  liter,  and  add  10  grams  of 
crystallized  ZnCl2.  Let  the  solution  settle  for  some  time,  and 
pour  off  for  use  the  nearly  clear  supernatant  liquid.  This  solu- 
tion is  very  sensitive  and  keeps  indefinitely. 

A  solution  of  1  gram  of  starch  in  200  c.c.  of  boiling  water  alone 
may  be  used,  but  it  must  be  made  fresh  every  day. 

For  a  more  sensitive  preparation  of  starch  see  page  225. 

Preparation  of  the  Iodine  Solution. — Weigh  on  a  watch-glass 
3.96  grams  of  pure  resublimed  iodine.  Put  it  into  a  liter  flask, 
add  about  6  grams  of  pure  potassium  iodide  (free  from  iodate) 
and  10  c.c.  of  water.  Let  stand  in  the  cold  until  all  the  iodine 
dissolves.  Then  dilute  to  1  liter. 

One  cubic  centimeter  of  this  solution  should  be  equivalent  to 
0.0005  gram  of  sulfur.  If  5  grams  of  metal  are  taken  for  the 
analysis  each  cubic  centimeter  of  iodine  solution  consumed  will  be 
equivalent  to  0.01  per  cent,  of  sulfur. 

In  the  reaction  H2S+2I  =  2HI-fS,  two  atoms  of  I  are 
equivalent  to  one  atom  of  S,  or  253.84  grams  of  1  =  32.06  grams 
of  S.  To  find  the  amount  of  I,  which  must  be  contained  in  1  c.c. 
to  give  a  solution  of  the  above  value  in  sulfur,  make  the  propor- 
tion 0. 005  :x  =  32.06: 253.84.  This  gives  x  =  0.003957  gram  per 
1  c.c.  or  3.96  grams  per  liter. 

Iodine  is  insoluble  in  water,  but  is  easily  and  rapidly  dissolved 
in  a  very  concentrated  solution  of  KI,  though  very  slowly  in  a  dilute 
one. 

The  iodine  solution  is  not  constant;  hence,  its  strength  must  be 
determined  frequently. 

Standardizing  the  Iodine  Solution. — Prepare  the  following 
solutions : 


THE  DETERMINATION  OF  Xl'LFUlt  101 

A.  Eight  grams  crystallized  sodium  thiosulfate  dissolved  in 
water  and  diluted  to  1  liter. 

B.  0.1531  gram  of  fused  potassium  dichromate  is  dissolved  in 
water  and  diluted  to  100  c.c.     If  more  convenient  this  solution 
may  be  made  by  diluting  10  c.c.  of  the  dichromate  solution  used 
in  the  iron  assay  (of  which  1  c.c.  equals  0.01  Fe)  to  57.42  c.c.; 
10  c.c.  of  this  solution  will  liberate  iodine  from  KI  equivalent 
to  0.005  gram  sulfur. 

Measure  with  a  pipette  10  c.c.  of  the  thiosulfate  solution  A 
into  a  beaker.  Add  100  c.c.  of  water  and  1  c.c.  of  starch  solution. 
Now  run  in  the  iodine  solution  from  a  burette  until  the  last  drop 
gives  a  decided  blue  color  not  disappearing  on  stirring.  Note 
exactly  the  amount  used.  Repeat  the  determination  two  or 
three  times  (the  results  should  agree  almost  exactly),  and  take 
the  average  as  the  amount  of  iodine  solution  equivalent  to  10  c.c. 
of  the  thiosulfate. 

Measure  10  c.c.  of  the  dichromate  solution  B  into  a  beaker. 
Add  50  c.c.  of  cold  water  and  then  about  0.5  gram  of  pure  KI. 
When  the  KI  is  dissolved  add  5  c.c.  of  concentrated  HC1. 

The  KI  must  be  free  from  iodate.  It  may  be  tested  by  dis- 
solving a  portion  in  water,  adding  some  starch  solution  and  a 
little  HC1.  The  liquid  should  not  show  more  than  a  trace  of 
blue  color  and  should  become  absolutely  colorless  on  the  addition 
of  a  small  drop  of  the  thiosulfate  solution.  The  acid  must  be 
free  from  chlorine  or  ferric  chloride.  When  diluted  it  should 
give  no  blue  color  on  the  addition  of  KI  and  starch. 

Let  the  mixture  stand  six  or  seven  minutes  without  warming 
(which  would  volatilize  iodine).  Dilute  to  100  c.c.  and  add  10 
c.c.  of  solution  A  and  1  c.c.  of  starch  solution.  Should  this  color 
the  liquid  blue,  add  10  c.c.  more  of  the  thiosulfate  solution  which 
will  make  it  colorless.  The  first  10  c.c.  is  usually  sufficient. 
Now  immediately  titrate  the  excess  of  thiosulfate  with  the  iodine 
solution,  adding  it  till  the  blue  color  is  developed.  Note  exactly 
the  volume  of  the  solution  used;  call  it  R. 

It  is  important  that  there  be  no  delay  between  the  addition 
of  the  solution  "A"  and  the  iodine  tit  ration  on  account  of  the 
presence  of  free  HC1  in  the  liquid.  Thiosulfate  is  slowly  decom- 
posed by  HOI  with  the  separation  of  sulfur  and  the  formation  of 
H^SOa  which  absorbs  twice  as  much  iodine. 


102  METALLURGICAL  ANALYSIS 

By  keeping  the  excess  of  thiosulfate  small  and  titrating  it 
within  one  minute,  correct  results  can  be  obtained. 

Now  the  difference  between  "R"  and  the  number  of  cubic 
centimeters  of  the  iodine  solution  that  are  equivalent  to  the 
number  of  cubic  centimeters  of  the  thiosulfate  solution  "A" 
added  to  the  dichromate  and  iodide  as  above,  is  the  volume  of 
the  iodine  solution  that  is  equivalent  to  0.005  gram  sulfur,  and 
0.005  divided  by  this  difference  is  the  value  in  sulfur  of  1  c.c.  of 
the  iodine  solution.  This  is  the  factor  by  which  to  multiply  the 
number  of  cubic  centimeters  taken  in  the  analysis  in  order  to 
obtain  the  amount  of  sulfur  present. 

Example. — Suppose  10  c.c.  of  solution  "A"  equals  10.6  c.c.  iodine 
solution.  Second,  that  20  c.c.  of  "A"  were  added  to  the  10  c.c.  of  "B" 
and  the  KI,  and  that  the  mixture  required  9.8  c.c.  of  iodine  solution 
on  the  titration  back;  that  is,  "R"  equals  9.8.  As  the  20  c.c.  of  "A" 
alone  would  equal  21.2  c.c.  of  iodine,  we  have  21.2  —  9.8  =  11.4,  which 
is  the  number  of  cubic  centimeters  of  iodine  solution  equivalent  to 
0.005  of  sulfur,  because  this  is  the  sulfur  equivalent  to  the  iodine  that 
is  liberated  from  the  KI  by  the  dichromate.  Further,  0.005  divided  by 
11.4  equals  0.000439,  which  is  the  amount  of  sulfur  to  which  1  c.c.  of 
the  iodine  solution  is  equivalent. 

The  reactions  upon -which  this  process  of  standardizing  depend  are: 

1.  2Na2S2O3  5H2O+2I  =  2NaI+Na2S406+5H20.     (The  crystallized 
thiosulfate  contains  five  molecules  of  water.) 

2.  K2Cr2O7+6KI+14HCl  =  8KCl+2CrCl2+7H2O+6I. 

Two  molecules  of  thiosulfate  weigh  496.64,  and  as  two  molecules 
of  thiosulfate  are  equivalent  to  two  atoms  of  iodine  (253.7)  we  have  the 
proportion  496.64:253.7  =  7.75:3.975,  7.75  being  the  amount  of  thio- 
sulfate which  should  be  dissolved  in  1  liter  to  give  a  solution  equiva- 
lent to  the  iodine,  but  as  it  is  desirable  that  this  solution  be  a  little 
stronger,  8  grams  are  actually  taken. 

The  thiosulfate  solution  is  not  constant,  hence  cannot  be  used  as  an 
absolute  check  on  the  iodine  solution,  but  only  as  a  means  of  comparing 
it  with  an  absolutely  known  amount  of  iodine.  This  definite  amount  of 
iodine  is  obtained  from  the  action  of  dichromate  on  an  excess  of  KI  in 
the  presence  of  HC1.  The  reaction  between  KI  and  K2Cr207  is  not 
instantaneous,  but  rapidly  becomes  complete. 

The  relation  between  the  K2Cr207  and  the  I  is  294.2  :  761.5,  hence 
0.01531  K2Cr207  will  liberate  0.0396  gram  of  iodine,  the  amount  which 
should  be  present  in  10  c.c.  of  the  iodine  solution  if  its  strength  were 
exactly  right. 


THE  DETERMINATION  OF  SULFUR  103 

The  operation  itself  consists  therefore  in  finding  how  much  of  the 
iodine  solution  to  be  standardized  is  required  to  titrate  the  amount  of 
the  thiosulfate  solution  which  is  equivalent  to  exactly  0.0396  gram  of 
iodine,  as  liberated  by  the  dichromate.  Thus  we  find  first  how  much 
of  the  iodine  solution  is  equal  to  a  certain  amount  of  the  thiosulfate 
solution;  second,  how  much  of  the  same  iodine  solution  is  equal  to  what 
is  left  after  the  same  amount  of  thiosulfate  has  been  acted  upon  by 
0.0396  gram  of  iodine,  and  the  difference  is  obviously  the  amount  of  io- 
dine solution  which  contains  0.0396  gram  of  iodine,  that  is  to  say,  will  be 
equivalent  to  0.005  of  S;  but  this  should  be  10  c.c.,  hence  the  difference 
between  10  and  the  amount  taken  is  the  amount  the  solution  is  off  the 
standard. 

The  only  precautions  to  be  noted  are  the  necessity  of  giving  time  for 
the  K2Cr207  to  react  on  the  KI  and  the  necessity  of  avoiding  heat  as 
iodine  is  readily  volatilized  from  this  solution. 

The  HC1  used  must  be  free  from  all  impurities  which  liberate  iodine 
from  KI(C12,  FeCl3,  CuCl2,  etc.). 

The  iodine  solution  may  also  be  standardized  against  a  sample  of 
iron  or  steel  similar  to  that  to  be  analyzed  in  which  the  sulfur  has  been 
accurately  and  repeatedly  determined  by  the  direct  oxidation  or  nitric 
acid  method. 

Treat  a  given  weight  of  the  metal  by  the  regular  process  and  deter- 
mine the  volume  of  the  iodine  solution  required  to  titrate  the  H2S 
evolved.  Then  from  the  known  sulfur  percentage  in  the  metal  calculate 
the  sulfur  value  of  1  c.c. 

Make  a  factor  of  correction  to  apply  to  the  iodine  solution.  This 
method  of  standardizing  has  the  advantage  of  causing  all  errors  of 
solution,  evolution  and  oxidation  to  affect  the  standard  and  sample 
alike,  and  makes  the  evolution  method  give  results  comparable  with  the 
gravimetric  method.  It  should  always  be  used  where  a  material  of 
generally  uniform  character  has  to  be  tested  as  manufactured.  As  the 
heat  treatment  and  the  nature  of  the  metal  cause  differences  in  the 
percentage  of  sulfur  evolved  as  H2S,  an  iodine  solution  standardized 
on  metal  should  never  be  used  for  a  metal  made  by  a  different  process, 
as  for  example,  one  standardized  on  pig-iron  for  steel.  (See  WILSON,  J. 
An.  and  App.  Chem.,  V,  439.)  When  the  sample  is  annealed  the 
method  of  standardization  does  not  make  so  much  difference. 

Cadmium  Solution. — Dissolve  4  grams  of  cadmium  chloride  in 
100  c.c.  of  water,  and  when  dissolved  add  an  equal  volume  of 
strong  ammonia. 

Apparatus. — This  is  shown  in  Fig.  4  and  consists  of  a  flask  F 


104 


ME  TA  LL  URGICA  L  A  A"  MA  "N  /  ,s' 


of  500  c;c.  capacity  and  fitted  with  a  rubber  stopper,  a  glass- 
funnel  tube  G  provided  with  a  stop-cock,  and  a  delivery  tube  H, 
in  which  are  blown  two  or  three  good-sized  bulbs.  These  bulbs 
serve  to  arrest  the  liquid  condensing  in  the  tube  and  allow  it  to 
return  to  the  flask  instead  of  working  over  into  the  absorption 
tubes.  A  water-cooled  condenser  is  better.  The  delivery  tube 
should  carry  the  gas  down  to  the  bottom  of  a  large  test-tube  I, 

8  in.  deep  and  1J4  in-  wide 
and  fitted  with  a  rubber 
stopper  through  which  a 
second  tube  carries  the  gas 
into  a  second  smaller  test- 
tube  J,  which  serves  to  catch 
any  absorbable  sulfur  com- 
pounds escaping  the  first  test- 
tube.  This  guard  tube  will 
rarely  show  any  sulfur.  Gas 
which  is  used  to  drive  over 
the  last  trace  of  H2S  is  in- 
troduced through  G  in  the 
top  of  which  is  fitted  a  one- 
hole  rubber  stopper  with  a 
glass  tube  connected  to  a 
source  of  gas. 

In  place  of  the  receiving 
cylinder  or  test-tube,  some 
use  a  large  flask,  diluting  the 
absorbing  liquid  correspond- 
ingly. The  titration  can  then  be  made  in  the  same  flask  with- 
out transferring  the  liquid.  When  the  bubbles  do  not  pass 
through  a  considerable  depth  of  liquid,  as  when  a  flask  is  used 
as  a  receiving  vessel,  it  is  best  to  have  the  delivery  tube  in  the 
vessel  end  in  the  form  of  a  funnel  to  keep  the  gas  longer  in  con- 
tact with  the  liquid. 

Amount  of  Metal  Taken. — This  may  be  5  grams  for  ordinary  irons  or 
10  grams  if  the  sulfur  is  very  low.  If  the  iodine  solution  is  a  little  "off 
the  standard" — that  is,  if  10  c.c.  are  equal  to  a  little  more  or  less  than 
0.005  gram  sulfur — it  is  more  convenient,  instead  of  correcting  each 
reading  by  multiplying  it  by  the  true  sulfur  value,  to  change  the  amount 


FIG.  4. 


THE  DETERMINATION  OF  SULFUR  105 

of  the  sample  taken  so  that  1  c.c.  of  the  iodine  solution  shall  represent 
0.01  per  cent,  of  sulfur. 

For  example:  Suppose  that  the  iodine  solution  is  too  weak  and  that 
1  c.c.  is  only  equal  to  0.0004854  gram  of  sulfur  instead  of  0.0005  gram. 
In  this  case  weigh  out  4.854  grams  of  the  metal  for  the  determination. 
Then  obviously  each  cubic  centimeter  of  the  iodine  solution  used  in  the 
titration  will  stand  for  0.01  per  cent,  of  sulfur,  and  the  calculations  which 
would  be  necessary  if  5  grams  had  been  taken  will  be  avoided. 

The  foregoing  method  of  applying  the  correction  factor  of  a  volumetric 
solution  to  the  amount  weighed  out  may  be  applied  to  any  similar 
process;  as,  for  example,  in  the  determination  of  iron,  phosphorus  or 
manganese;  and  where  many  analyses  are  to  be  made  will  save  much 
time  as  well  as  diminish  the  chances  of  error  involved  in  the  calculations. 

Process  for  the  Analysis. — Transfer  the  weighed  metal  to  the 
flask  and  add  about  2  grams  of  pure  precipitated  CaCO3.  Pour 
5  c.c.  of  the  cadmium  solution  into  the  absorbing  tube  and  add 
to  it  10  to  15  c.c.  of  strong  NH4OH.  Now  fill  the  tube  with 
water  to  a  depth  of  6  in.  Put  50  c.c.  of  HC1,  sp.  gr.  1.19,  into 
the  bulb  of  the  funnel  tube.  Run  in  the  acid  slowly  until  the 
CaCO3  is  all  dissolved,  then  run  the  acid  in  rapidly  but  avoid  so 
rapid  an  evolution  of  gas  as  to  throw  the  liquid  out  of  the  tube 
or  make  bubbles  large  enough  to  fill  the  tube.  When  the  evolu- 
tion of  gas  slows  up,  heat  the  flask  hot  enough  to  make  the 
evolution  of  gas  rapid,  but  do  not  boil  until  the  iron  is  all  dis- 
solved as  this  would  cause  too  much  acid  to  distill  over.  When 
the  iron  is  dissolved,  boil  the  solution  for  several  minutes.  For 
the  best  results  pass  a  stream  of  hydrogen  or  carbon  dioxide  or 
natural  gas  (purified  by  passing  through  NaOH  solution)  through 
the  apparatus  to  drive  out  all  traces  of  H2S.  The  solution  in 
the  tube  must  be  kept  alkaline  by  adding  more  ammonia  if  neces- 
sary. The  CdS  should  separate  as  a  yellow  precipitate.  If  it 
is  pale  in  color,  the  sulfur  is  not  being  evolved  properly  as  H2S. 

When  using  concentrated  HC1,  a  considerable  amount  of  acid 
distills  over  unless  a  water-cooled  condenser  is  used,  but  by  using 
sufficient  NH4OH,  it  will  do  no  harm.  After  the  liquid  has  been 
boiled  several  minutes  and  no  more  gas  is  coming  over,  open  the 
stop-cock  in  the  funnel  tube,  remove  the  lamp,  and  detach  the 
delivery  tube.  Empty  the  absorbing  tube  into  a  large  flask, 
wash  it  and  the  delivery  tube  well  with  water  and  pour  the  wash- 


106  METALLURGICAL  ANALYSIS 

ings  into  the  flask.  Now  add  300  or  400  c.c.  of  cold  water,  and 
then  HC1  enough  to  make  the  solution  acid  and  10  or  15  c.c.  more, 
which  should  dissolve  the  precipitated  CdS.  Now  add  1  c.c.  of 
the  starch  solution  and  titrate  immediately  with  the  iodine 
solution,  adding  it  until  the  last  drop  changes  the  opalescent 
liquid  to  a  deep  blue  not  disappearing  on  standing  two  or  three 
minutes. 

The  number  of  cubic  centimeters  used,  after  correction  for 
standard,  will  give  the  amount  of  sulfur  in  hundredths  of  a  per 
cent.  Always  make  a  blank  test  on  the  reagents;  they  will  usu- 
ally consume  a  little  iodine  which  must  be  deducted  from  that 
used  in  the  analysis. 

Notes  on  the  Process. — Use  pure  gum-rubber  tubing  in  the  con- 
nections. White  or  red  rubber  may  contain  metallic  sulfides  evolving 
H2S  when  acted  upon  by  the  HC1  vapor,  thus  causing  errors. 

It  is  essential  that  the  process  be  carried  through  promptly.  There 
should  be  no  delay  in  titrating.  If  the  solution  containing  the  CdS  be 
allowed  to  stand  it  may  lose  H2S  or  the  sulfides  may  oxidize.  This  is 
especially  important  after  the  addition  of  HC1,  as  the  free  H2S  will 
oxidize  very  rapidly  on  standing.  Zinc  salts  (acetate  or  sulfate)  may 
be  used  in  the  place  of  cadmium  with  satisfactory  results. 

The  Use  of  NaOH  instead  of  CdCl2. — The  process  is  conducted  as 
before,  except  that  the  absorption  tube  is  filled  with  80  c.c.  of  a  15  per 
cent,  solution  of  NaOH.  After  the  evolution  of  the  gas,  wash  out  the 
tube  into  a  large  beaker,  dilute  as  before  with  cold  water,  acidify,  add 
starch  solution  and  titrate.  Most  caustic  soda  contains  a  little  iron 
as  ferric  hydroxide,  which  dissolves  in  the  concentrated  solution  but 
separates  on  dilution;  hence,  the  15  per  cent,  soda  solution  should  be 
prepared  some  time  before  use,  and  the  clear  liquid  decanted  from  the 
precipitate  which  usually  settles.  Test  the  solution  also  for  nitrites 
and  hypochlorites  by  acidifying  a  portion  with  HC1,  and  then  adding 
KI  and  starch  paste.  It  must  show  no  blue  color.  In  acidifying  the 
soda  solution  before  titration  add  a  drop  of  phenolphthalein  solution, 
and  then  add  the  HC1  till  the  red  color  is  discharged.  The  HC1  must 
be  pure.  It  will  occasionally  contain  traces  of  S02  which  would  of 
course  vitiate  the  results. 

The  cadmium  method  is  sometimes  modified  by  filtering  off  the  CdS 
and  putting  the  filter  and  precipitate  into  a  large  volume  of  water, 
adding  HC1  and  titrating.  This  avoids  the  presence  of  a  large  amount 
of  ammonium  salts  and  of  any  hydrocarbons  absorbed  in  the  liquid. 
It  has  been  claimed  that  these  act  slightly  on  the  iodine.  The  advantage 


THE  DETERMINATION  OF  SULFUR  107 

of  this  modification  is  very  slight  if  any,  as  the  evolution  process  usu- 
ally gives  low  results  any  way. 

The  method  as  above  given  is  very  rapid,  but  gives  accurate  results 
only  on  those  samples  which  give  up  all  their  sulfur  as  H2S.  The 
following  method,  first  proposed  by  Walters  and  Miller,  and  modified 
by  many  others,  is  the  method  elaborated  by  ELLIOT  (J.  Iron  and  Steel 
Inst.,  1911,  p.  412)  and  is  good  for  all  kinds  of  samples. 

Annealing-evolution  Process. — Five  grams  of  the  sample  are 
mixed  with  0.25  gram  of  pure  finely  powdered  anhydrous  po- 
tassium-ferrocyanide,  and  wrapped  in  one  11-cm.  filter  paper 
if  the  sample  is  a  graphitic  iron,  or  two  papers  if  it  is  a  steel  or 
white  iron,  placed  in  a  small  porcelain  crucible,  covered  with  a 
lid,  and  annealed  at  750°  to  850°C.  (just  above  the  recalescence 
temperature)  for  20  minutes  in  a  muffle.  The  crucible  is  re- 
moved and  allowed  to  cool  slowly.  The  drillings  should  still  be 
covered  with  charred  paper.  The  drillings  are  now  transferred 
to  the  evolution  flask  and  the  process  continued  as  described  for 
the  evolution  process  above.  Instead  of  using  an  alkaline  cad- 
mium chloride  solution  Elliot  uses  the  following:  20  grams  of 
CdCl2  are  dissolved  in  water  and  NH4OH  added  until  the 
Cd(OH)2  dissolves.  Then  acetic  acid  is  added  until  the  liquid  is 
acid,  then  20  c.c.  more.  The  solution  is  diluted  to  1000  c.c. 
Fifty  cubic  centimeters  are  used  for  each  determination.  Ac- 
cording to  Elliot  this  solution  does  not  dissolve  hydrocarbons, 
phosphides,  etc.,  as  alkaline  solutions  do. 

This  process  gives  good  results  even  on  alloy  steels  and  titan- 
iferous  pig-iron. 

REFERENCES  ON  THE  EVOLUTION  PROCESS: 
ELLIOT,  J.  Iron  Steel  Inst.,  1911,  p.  412. 
ORTHEY,  Z.  angew  Chem.,  1359-64,  1393-9. 
KINDER,  Stahl  u.  Eisen,  XXVIII,  249-54. 

Trans.  Am.   Inst.    Mining  Eng.,   X,   187  (cadmium),  and  XII,  507 
(bromine). 

BROWN'S  METHOD  WITH  POTASSIUM  PERMANGANATE 

This  is  the  least  troublesome  of  the  gravimetric  evolution  methods. 
It  is  accurate  for  those  metals  which  evolve  their  sulfur  as  H2S.  The 
H2S  is  absorbed  by  an  alkaline  solution  of  KMn04.  This  is  a  more 
energetic  absorbent  than  the  neutral  solution  originally  proposed  by 


108  METALLURGICAL  ANALYSIS 

Dr.  Drown,  hence  the  gas  can  be  sent  through  the  liquid  much  more 
rapidly  without  danger  of  any  sulfur  escaping  absorption. 

As  the  rubber  stoppers  and  tubes  used  in  the  apparatus  may  contain 
sulfur  they  must  be  kept  from  contact  with  the  absorbing  solution. 
They  should  be  prepared  for  use  by  first  boiling  them  for  some  time 
in  a  dilute  solution  of  NaOH,  then  rubbing  them  well  to  remove  any 
crust  from  the  surface,  and  finally  washing  them  thoroughly  with  water 
and  dilute  HC1. 

Process  of  Analysis. — Weigh  5  or  10  grams  of  the  drillings  ac- 
cording to  the  percentage  of  sulfur  contained  in  the  metal,  into 
the  flask.  Put  into  the  first  test-tube  in  the  absorbing  train 
30  c.c.  of  a  solution  of  potassium  permanganate,  5  grams  to  the 
liter,  and  30  c.c.  of  a  10  per  cent,  solution  of  pure  sodium  hydrox- 
ide. Charge  the  second  tube  in  the  same  way,  using  half  the 
amounts.  Add  water  to  the  tubes  until  they  are  about  half  filled 
by  the  liquid ;  there  should  be  a  space  of  3  or  4  in.  above  the  liquid 
in  each  tube.  Now  connect  up  the  apparatus,  put  50  or  60  c.c. 
of  concentrated  HC1  into  the  funnel  tube,  and  cautiously  run  this 
into  the  flask.  This  should  be  done  rapidly  but  not  so  as  to 
cause  such  an  evolution  of  gas  as  to  form  very  large  bubbles  in 
the  tubes,  or  to  throw  the  absorbing  liquid  up  against  the  corks. 
As  the  absorbing  liquid  is  alkaline,  the  evolution  of  the  gas  can  be 
quite  rapid  without  danger  of  H2S  escaping  absorption,  and  the 
more  rapidly  the  iron  is  dissolved  the  larger  the  percentage  of 
the  sulfur  which  appears  to  be  evolved  in  an  absorbable  form. 
When  the  action  becomes  slow  and  the  iron  is  nearly  all  dissolved, 
bring  the  contents  of  the  flask  to  boiling  and  boil  until  the  liquid 
in  the  first  tube  grows  quite  warm  and  MnC>2  begins  to  separate. 
The  steam  will  drive  over  all  the  H2S  and  also  to  some  extent 
carry  over  difficultly  volatile  sulfur  compounds,  leaving  the  resi- 
due in  many  cases  practically  free  from  sulfur.  Now  remove  the 
lamp,  being  careful  to  immediately  open  the  stop-cock  of  the 
funnel  tube  so  as  to  admit  air  to  the  flask  as  it  cools,  or  a  vacuum 
may  form  and  the  contents  of  the  test-tubes  be  drawn  back  into 
the  flask. 

Disconnect  the  test-tubes,  empty  them  into  separate  beakers, 
washing  out  both  the  connecting  tube  and  the  test-tubes  with 
water.  Any  MnO2  adhering  to  the  tubes  should  be  dissolved  off 
with  a  little  HC1,  and  the  solution  added  to  the  liquid  from  the 
test-tubes.  A  little  oxalic  acid  should  be  added  to  the  HC1  so 


THE  DETERMINATION  OF  SULFUR  109 

used.  The  contents  of  the  second  tube  should  be  alkaline  at  the 
end  of  the  process  though  the  HC1  distilling  over  will  probably 
have  neutralized  the  alkali  in  the  first  tube  and  dissolved  most  of 
the  Mn02.  Now  heat  the  contents  of  the  beakers,  and  if  not 
already  acid  add  a  slight  excess  of  HC1  which  may  cause  MnO2 
to  separate.  Drop  in  a  solution  of  oxalic  acid  carefully  until  the 
MnO2  is  all  dissolved  and  the  solutions  are  colorless.  Add  to 
each  beaker  15  c.c.  of  a  10  per  cent,  solution  of  BaCl2,  settle, 
filter,  wash  and  weigh  the  BaSO4  as  usual.  The  liquid  from  the 
second  tube  should  show  no  more  than  a  trace  of  BaSO-*.  Filter 
this  in  with  the  first  precipitate.  Should  the  second  tube  show 
much  precipitate  repeat  the  process,  evolving  the  gas  more 
slowly.  Run  a  careful  blank  on  the  permanganate,  soda,  acids, 
etc.,  using  the  same  amount  of  each  as  is  taken  in  the  analysis, 
and  deduct  the  weight  of  the  BaSO4  found  in  this  (due  to  im- 
purity of  reagents)  from  that  found  in  the  analysis. 

Instead  of  using  concentrated  HC1  in  the  process,  many  prefer 
to  use  the  acid  diluted  with  its  own  volume  of  water.  It  is 
easier  to  conduct  the  process  in  this  way,  as  less  of  the  acid  dis- 
tills over  into  the  tubes,  but  it  is  a  little  more  liable  to  leave  sulfur 
behind  in  the  residue. 

Aspiration  of  air  or  CO2  through  the  flask  to  remove  the  last 
traces  of  H2S  is  unnecessary  with  the  small  percentages  of  sulfur 
found  in  iron  and  steel. 

Examination  of  the  Residue  in  the  Flask  for  Sulfur. — Filter 
the  contents  of  the  flask  through  a  9-cm.  filter,  wash  the  residue 
thoroughly  and  dry  it  at  a  temperature  not  exceeding  100°C. 
Open  out  the  filter  and  brush  the  residue  into  a  small  beaker. 
Add  10  c.c.  of  concentrated  HNO3  and  a  small  crystal  of  KC103. 
Boil  down  to  dryness,  take  up  by  heating  with  5  c.c.  of  concen- 
trated HC1,  dilute  to  30  or  40  c.c.,  filter  and  add  5  c.c.  of  BaCl2 
solution  to  the  filtrate.  Let  stand  till  any  precipitate  of  BaSO4 
settles,  filter  it  off  and  weigh  it. 

The  residue  may  also  be  treated  by  fusion  exactly  as  an  iron 
ore,  of  course  using  smaller  quantities  of  fluxes. 

REFERENCES: 

DROWN,  Trans.  Am.  Inst.  Mining  Eng.,  II,  p.  224. 
AUCHY,  J.  Am.  Chem.  Soc.,  1896,  p.  404. 


110  METALLURGICAL  ANALYSIS 

Special  Method  for  Sulfur  in  High-percentage  Alloy  Steels.— In 
these  materials  Miiller  and  Diethelm  determine  the  sulfur  in  connection 
with  the  direct  combustion  method  for  carbon.  The  steel  is  burned 
in  an  electric  furnace  at  1100°C.  Following  the  combustion  furnace 
but  on  the  same  tube  is  a  second  heating  apparatus  to  heat  the  tube  to 
350°C.  and  in  this  part  a  couple  of  boats  are  placed  to  hold  8.5  grams 
of  PbO2.  The  sulfur  is  retained  by  the  Pb02  which  is  removed  and 
boiled  with  Na2C03.  The  sulfur  is  then  determined  in  the  solution  by 
precipitating  with  BaCl2  from  an  acid  solution.  See  Z.  angew.  Chem., 
XXIII,  2114. 

Sulfur  in  ferrovanadium  cannot  be  determined  by  the  evolution 
method;  it  must  be  determined  by  the  gravimetric  method.  (CLARK, 
Met.  Chem.  Eng.,  XI,  256.) 


CHAPTER  VIII 

THE  DETERMINATION  OF  CARBON  IN  PIG-IRON  AND 

STEEL 

The  carbon  in  gray  pig-iron  occurs  mostly  as  mechanically  admixed 
graphite,  with  a  small  proportion  as  a  carbide  Fe3C,  called  "Cementite." 
In  white  iron  and  chilled  iron,  as  well  as  in  steel,  the  carbon  exists  chiefly 
either  as  a  carbide  or  in  solid  solution,  forming  the  phase  known  as 
"Austensite"  or  its  transition  form  called  "Martensite."  Malleable 
iron  (made  by  prolonged  annealing  of  white  iron)  contains  carbon  in  a 
more  finely  divided  form  than  graphite,  but  not  in  combination  with 
iron. 

When  an  iron  containing  carbon  in  these  different  conditions  is  dis- 
solved in  hot  HC1  or  HN03,  sp.  gr.  1.2,  the  graphite  and  amorphous 
carbon  are  entirely  left  as  a  black  residue  which  can  be  filtered  off, 
while  the  combined  carbon  stays  in  solution  entirely  if  HN03  is  used, 
but  passes  off  partly  as  hydrocarbon  if  HC1  is  used. 

Methods  are  here  given  for  the  determination  of  " total  carbon," 
"combined  carbon"  and  " graphitic  carbon." 

DETERMINATION  OF  TOTAL  CARBON 

The  total  carbon  is  usually  determined  by  one  of  the  following 
methods: 

A.  Direct  oxidation  of  the  iron  and  carbon  in  some  form  of  a  furnace 
in  a  current  of  oxygen.     The  drillings  may  or  may  not  be  mixed  with 
an  oxidizing  agent  such  as  Pb3O4  in  order  to  insure  complete  combus- 
tion, or  with  some  flux  to  permit  the  oxygen  to  completely  oxidize  the 
iron. 

The  CC>2  liberated  may  be  caught  in  an  alkaline  solution  and  weighed, 
or  it  may  be  precipitated  as  BaC03  which  is  filtered  off  and  weighed, 
or  it  may  be  absorbed  in  an  alkaline  solution  of  known  strength  and 
the  excess  of  alkali  titrated  by  standard  acid,  or  finally  the  COz  may  be 
measured  by  gas  volumetric  methods.  The  last  method  is  not  widely 
used. 

B.  The  iron' is  dissolved  in  a  solvent,  generally  K2CuCl4,  which  leaves 
all  the  carbon,  whether  free  or  combined,   undissolved.     The  carbon 
is  filtered  off  on  asbestos  and  burned  to  COo  and  determined  as  above. 

Ill 


112  METALLURGICAL  ANALYSIS 

The  burning  or  oxidation  of  the  carbon  may  be  done  either  in  a  fur- 
nace (including  such  devices  as  the  Shimer  crucible)  or  it  may  be  done 
by  a  wet  process,  as  by  combustion  in  sulfuric  and  chromic  acids. 

C.  Solution  and  simultaneous  oxidation   of  the   sample  in   sulfuric, 
chromic  and  phosphoric  acids,  the  C(>2  being  either  measured  or  weighed. 

D.  When  the  carbon  is  present  entirely  as  combined  carbon  as  in 
steel  it  may  be  determined  colorimetrically. 

DIRECT  COMBUSTION  METHOD  FOR  CARBON 

This  is  the  method  most  widely  in  use.  When  used  with  proper 
precaution  it  is  very  accurate  and  very  rapid.  A  complete  determina- 
tion can  be  made  in  25  minutes  or  less. 

The  complete  combustion  of  steel  drillings  is  dependent  upon  the 
temperature  of  the  furnace.  With  sufficiently  high  temperature  any 
ordinary  steel  can  be  completely  burnt  in  a  stream  of  oxygen  without 
using  red  lead.  The  temperature  ordinarily  attainable,  however,  is 
not  sufficient  to  burn  completely  such  alloys  as  ferro-chrome,  etc.,  and 
such  samples  must  be  mixed  with  red  lead.  Pig-iron  also  requires 
some  red  lead.  The  drillings  should  not  be  too  coarse  or  combustion 
is  apt  to  be  incomplete.  They  should  go  through  a  20-mesh  sieve, 
although  the  writer  has  had  no  difficulty  with  coarser  samples  when 
the  temperature  of  the  furnace  was  1050°C.  Some  chemists  place  the 
drillings  in  as  compact  a  mass  as  possible  in  order  that  the  heat  of  the 
burning  iron  may  keep  it  at  a  high  temperature.  This  will  cause  the 
mass  to  fuse  unless  the  flow  of  oxygen  is  carefully  regulated,  and  enclose 
particles  of  unburned  iron  and  also  destroy  the  boat.  The  writer  pre- 
fers to  scatter  the  drillings  along  the  boat  and  then  maintain  a  high 
enough  temperature  in  the  furnace  to  insure  complete  combustion. 
Some  chemists  mix  the  drillings  with  ignited  alumina  or  Mn304  in  order 
to  keep  the  drillings  separated. 

Such  alloys  as  ferro-chrome,  ferro-molybdenum,  ferro-tungsten  and 
the  "high  speed  steels"  cannot  be  accurately  analyzed  for  carbon  by 
the  methods  involving  solution  in  K2CuCl4  as  hydrocarbons  are  evolved 
upon  solution.  So  they  must  be  analyzed  by  some  form  of  direct  com- 
bustion. (See  JOHNSON,  "Chemical  Analysis  of  Special  Steels,  Steel 
Making  Alloys  and  Graphites,"  p.  132  et  seq.) 

Apparatus  Used. — Either  gas-heated  furnaces  or  electrically 
heated  furnaces  may  be  used.  The  writer  prefer^  the  electric 
furnace  because  of  the  ease  with  which  the  temperature  may  be 
controlled  and  because  it  does  not  heat  up  the  laboratory  notice- 
ably. The  bars  on  the  rheostat  are  numbered  and  this  apparatus 


CARBON  IN  PIG-IRON  AND  STEEL 


113 


is  calibrated  so  that  each  number  corresponds  to  a  certain  tem- 
perature in  the  furnace.  This  avoids  the  continual  use  of  a 
pyrometer.  Fig.  5  shows  the  apparatus. 

A  is  an  oxygen  tank  which  delivers  oxygen  at  a  constant 
pressure. 

B  is  a  silica  tube  containing  palladiumized  asbestos.  It  is 
heated  with  a  wing  top  burner  and  burns  any  hydrocarbons  con- 
tained in  the  oxygen.  With  good  oxygen  it  may  be  omitted. 

C  is  a  bottle  containing  KOH  solution. 

D  is  a  bottle  tube  containing  sulfuric  acid. 


FIG.  5. 


E-F  is  a  "U"  tube  containing  soda-lime  (E)  in  one  limb  and 
CaCl2  (F)  in  the  other. 

G  is  a  Hoskin's  electric  furnace.  The  tube  is  of  fused  silica 
J^  in.  internal  diameter.  The  tube  is  empty  to  the  middle  be- 
yond which  is  a  roll  of  CuO  wrapped  in  asbestos  paper,  then  a 
plug  of  palladiumized  asbestos,  then  a  boat  containing  PbCrO4. 
The  copper  oxide  and  the  palladiumized  asbestos  insure  the  com- 
bustion of  any  CO  to  CC>2.  As  a  rule  they  are  not  needed  but  it 
is  safest  to  use  them  in  case  of  the  combustion  of  pig-iron.  CuO 
and  PbCr04  must  not  be  placed  in  contact  with  the  silica  tube 
as  they  will  destroy  it.  [The  PbCrO4  is  placed  where  the  tube 
attains  only  a  dull  red  heat;  it  must  not  be  heated  to  the  full 
heat  of  the  furnace.]  The  CuO  should  be  in  the  hot  part  of  the 
furnace. 

H  is  a  "U"  tube  containing  granular  zinc  in  the  left  side  and 

8 


114 


METALLURGICAL  ANALYSIS 


3  A* 


CaCl2  in  the  right.  The  zinc  together  with  the  PbCr04  remove 
the  sulfur  fumes  resulting  from  burning  the  sample.  The  zinc 
also  removes  chlorine  and  litharge  fumes.  The  CaCl2  insures 
that  the  gas  enters  the  weighing  apparatus  with  the  same  degree 
of  dryness  as  it  leaves  it.  Otherwise  it  will  gain  or  lose  weight. 
I  is  the  weighing  apparatus.  There  are  many  kinds,  but  the 
writer  prefers  a  Liebig  bulb  to  which  is  attached  a  2  in.  "U"  tube 
containing  soda  lime  in  the  side  next  to  the  KOH  bulb  and  CaCl2 
in  the  other  side  with  a  plug  of  cotton  separating  them.  The 
tubes  at  the  entrance  and  the  exit  of  the  weighing  apparatus 

should  be  softened  until  nearly  closed. 
The  gas  should  bubble  through  all 
the  bulbs  of  the  Liebig  apparatus,  then 
pass  over  the  soda  lime,  then  over  the 
CaCl2.  See  Fig.  9,  page  127. 

J  is  a  guard  tube  containing  CaCl2 
in  the  left  side  and  soda  lime  in  the 
right  side. 

K  is  an  aspirator  to  draw  the  gas 
through  and  also  to  indicate  how  much 
has  been  aspirated. 

The  KOH  used  in  the  weighing  ap- 
paratus is  a  30  per  cent,  solution.  It 
should  be  previously  heated  to  boiling 
with  a  little  KMnO4  to  oxidize  the  iron 
which  it  generally  contains.  Other- 
wise it  will  absorb  oxygen  during  the 
aspiration  and  gain  weight.  The 
weighing  bulbs  should  be  washed  off 
after  they  are  filled  and  then  wiped  dry.  If  the  entrance  and 
exit  tubes  are  nearly  closed  as  directed,  there  is  no  need  of  rub- 
ber caps  on  them  during  weighing. 

The  gas  holder  shown  in  Fig.  6  was  designed  by  Professor  Lord 
some  years  ago;  it  has  the  advantage  of  keeping  the  gas  at  con- 
stant pressure,  a  point  of  some  importance  in  combustion  work 
as  variations  in  pressure  affect  the  rate  of  flow  through  the 
furnace. 

A  is  a  drum  of  tinned  copper  14  in.  in  diameter  and  24  in.  high. 
It  is  provided  with  a  stop-cock,  H,  for  drawing  out  the  gas  and  a 


FIG.  6. 


CARBON  IN  PIG-IRON  AND  STEEL  115 

gage,  B,  for  showing  the  level  of  the  water  in  the  drum.  I  is 
an  opening  near  the  bottom  of  the  drum  for  letting  out  the  water 
when  filling  the  tank  with  gas.  When  using  the  tank  this  open- 
ing is  closed  with  a  good  rubber  stopper.  The  gas  is  run  into 
the  tank  through  the  cock  H  or  by  a  tube  inserted  into  I  and  small 
enough  to  allow  the  water  to  escape  around  it.  The  arrangement 
for  forcing  the  gas  out  of  the  tank  is  as  follows :  Water  is  kept 
running  into  the  cup,  E,  on  top  of  the  drum  at  such  a  rate  as  to 
overflow  continuously  through  one  of  the  side  openings,  F,  into 
a  sink.  The  head  of  water  on  the  gas  is  determined  by  the  open- 
ing selected,  the  others  being  closed  by  corks.  From  the  bottom 
of  this  cup  a  pipe,  D,  runs  down  into  the  drum  and  into  an  inte- 
rior cup,  C,  which  fills  with  water  and  overflows  through  the 
pipe  G  into  the  bottom  of  the  tank. 

It  will  be  seen  that  the  water  will  in  this  way  fill  the  tank  and 
force  out  the  gas  and  yet  the  "head"  on  the  gas  will  always  be 
the  difference  in  the  level  between  the  water  in  the  cupr  E,  and 
that  in  the  cup,  C,  inside  the  tank  and  thus  remain  constant. 
The  interior  cup  can  be  made  smaller  than  shown  in  the  figure; 
it  is  only  necessary  that  it  have  volume  enough  to  allow  for  the 
expansion  and  contraction  of  the  gas  due  to  the  ordinary  changes 
of  temperature. 

The  oxygen  may  be  passed  into  the  train  directly  from  a  high 
pressure  oxygen  cylinder  but  the  writer  prefers  to  use  the  above. 

Process  of  Analysis. — After  the  furnace  is  heated  up  to  1000°C., 
the  aspirator  is  opened  while  the  tube  at  the  extreme  left  is 
closed.  If  the  apparatus  is  tight  no  bubbles  will  pass  through 
the  KOH  bulb  after  a  few  minutes.  If  it  is  not  tight,  it  of  course 
must  be  made  so.  Now  aspirate  oxygen  or  air  through  at  the 
rate  of  four  or  five  bubbles  per  second  for  several  minutes,  detach 
the  weighing  apparatus  and  weigh.  Again  attach  the  weighing 
apparatus,  aspirate  through  1000  c.c.  of  oxygen,  detach  and  again 
weigh.  There  should  not  be  either  gain  or  loss  in  weight.  If 
there  is  none,  everything  is  ready  for  the  determination. 

Weigh  2  grams  of  the  proper  sized  sample.  Pour  into  a  boat, 
preferably  one  of  alundum  or  silica,  pure  alundum  sand  enough  to 
cover  the  bottom  of  the  boat  and  heap  up  against  the  sides  when 
a  trough  is  made  in  the  sand  with  a  spatula.  The  sand  should 
be  fine  enough  to  pass  through  a  30-mesh  sieve.  Scatter  the 


116  METALLURGICAL  ANALYSTS 

sample  drillings  in  this  trough  so  that  they  do  not  heap  up  above 
the  top  of  the  boat,  and  do  not  touch  the  boat.  Open  the  furnace 
tube  at  the  left  end,  quickly  push  the  boat  to  the  middle  of  the 
furnace,  and  close  the  tube.  Start  the  aspirator  and  connect 
to  the  oxygen  supply.  As  soon  as  the  oxygen  gets  to  the  sample 
combustion  commences  rapidly,  and  the  oxygen  will  flow  in 
with  a  rush,  causing  such  rapid  combustion  of  the  iron  that  it  will 
fuse  unless  the  flow  of  oxygen  is  regulated.  It  should  be  so 
regulated  that  2  grams  of  iron  burn  completely  in  three  to  four 
minutes.  The  end  of  the  combustion  is  shown  when  the  oxygen 
ceases  to  flow  rapidly.  If  the  combustion  has  been  complete, 
about  650  c.c.  of  oxygen  will  have  been  used.  During  the 
combustion  period,  very  little  oxygen  will  be  flowing  through  the 
potash  bulbs,  but  a  small  amount  should  do  so.  After  the  com- 
bustion period,  continue  to  pass  oxygen  or  air  through  for  15 
minutes.  Detach  the  weighing  apparatus  and  weigh.  The 
weighing  must  be  done  promptly  when  the  ends  are  not  capped. 
If  the  apparatus  is  weighed  filled  with  oxygen  it  should  be  capped, 
if  filled  with  air  the  caps  are  not  necessary.  The  increase  in 
weight  multiplied  by  Y\\  gives  the  amount  of  carbon  present. 

In  order  to  save  oxygen,  air  may  be  aspirated  through  before 
and  after  the  combustion,  but  this  takes  more  time.  The 
bulbs  may  be  filled  with  air  by  detaching  them  from  the  furnace 
and  drawing  through  them  air  dried  by  first  passing  over  calcium 
chloride.  If  the  bulbs  are  weighed  with  oxygen  in  them  before 
the  combustion  they  must  also  be  weighed  with  the  same  gas 
after  the  combustion.  They  should  be  counterpoised  on  the 
balance  with  another  set. 

The  weighing  apparatus  is  again  attached,  the  boat  and  its 
contents  removed  from  the  furnace,  and  all  is  ready  for  the  next 
determination.  The  potash  bulbs  can  be  used  20  to  40  times 
before  they  need  to  be  refilled. 

In  the  case  of  pig-iron  and  many  alloys,  the  process  is  just  the 
same  as  above  given,  except  that  an  equal  weight  of  red  lead  is 
mixed  with  the  drillings. 

Notes  on  the  Process. — The  ends  of  the  combustion  tube  should  be 
kept  cool  by  being  wrapped  with  asbestos  cloth,  the  ends  of  which  dip 
in  a  beaker  of  water.  It  is  also  well  to  have  a  plug  of  asbestos  in  front 


CARBON  IN  PIG-IRON  AND  STEEL  117 

of  the  stoppers  to  protect  them  from  heat  radiation  from  the  walls  of 
the  tube. 

Steel  drillings  and  red  lead  should  not  be  spilled  in  the  tube  as  they 
combine  with  the  silica  and  destroy  the  tube.  It  is  well  to  have  a 
little  silica  sand  scattered  about  the  bottom  of  the  tube  to  combine 
with  spilled  material. 

The  sand  and  red  lead  used  should  be  thoroughly  ignited  before  use 
in  order  to  remove  any  carbon.  The  same  is  true  of  the  boat. 

The  boats  used  may  be  molded  of  clay  or  may  be  made  of  silica, 
porcelain,  alundum  or  platinum.  The  writer  prefers  the  alundum  or 
silica  boats.  Each  one  should  last  for  many  determinations  wrhen 
properly  protected  with  sand.  Boats  made  of  molded  asbestos  are 
sometimes  used. 

While,  as  a  rule,  it  is  not  necessary  to  use  GuO  in  the  furnace  it  is 
safest  to  do  so  in  order  to  burn  any  CO  which  may  have  been  formed. 
It  may  be  used  without  injuring  the  silica  tube  as  follows:  A  roll  of 
CuO  gauze  is  wrapped  with  asbestos  paper  and  then  placed  in  the  tube 
on  pieces  of  broken  alundum  boats.  The  CuO  should  be  well  within 
the  furnace.  A  plug  of  palladiumized  asbestos  completes  the  pre- 
cautions for  complete  combustion  of  any  CO  possibly  present,  and  also 
protects  the  stopper  on  the  exit  side  of  the  furnace  from  heat  radiation. 
The  palladiumized  asbestos  is  made  as  directed  on  page  285. 

The  temperature  of  the  furnace  should  be  not  less  than  950°  and 
preferably  as  high  as  1050°C.  At  lower  temperatures  combustion  of 
the  sample  is  not  complete. 

Instead  of  a  silica  tube,  a  porcelain  one  may  be  used.  Porcelain 
breaks  more  easily  than  the  silica  tube  when  heated  or  cooled.  Plat- 
inum tubes  are  used  in  some  works  and  are  very  desirable  but  their  first 
cost  is  very  high. 

It  must  be  remembered  that  the  CO  and  C02  dissolved  in  steel  will 
be  included  in  the  carbon  obtained  by  this  method.  This  may  make 
the  results  as  much  as  0.05  per  cent,  too  high. 

If  a  large  soda-lime  tube  or  bottle  is  used  to  absorb  the  C02,  and  P208 
for  drying  the  gas,  the  oxygen  may  be  passed  through  as  fast  as  400 
c.c.  per  minute  and  the  combustion  and  absorption  may  be  done  in  six 
minutes.  Special  precaution  is  necessary  to  protect  the  tube  from  spat- 
tered oxide  of  iron.  (FLEMING,  Chem.  Eng.,  XVII,  80.) 

•    BARIUM  CARBONATE  METHOD  FOR  CARBON 

On  damp  days  it  is  difficult  to  weigh  a  large  absorption  apparatus 
accurately  on  account  of  the  varying  amounts  of  moisture  on  the  surface 


118  METALLURGICAL  ANALYSIS 

of  the  glass  at  different  weighings.  Consequently  many  chemists  pre- 
fer to  absorb  the  carbon  dioxide  in  barium  hydroxide  solution  and  weigh 
or  titrate  the  BaC03.  This  is  carried  out  as  follows: 

Process  of  Analysis. — In  place  of  the  weighing  apparatus  (pot- 
ash bulbs  or  soda-lime  tube)  attach  a  Meyer  tube  (M,  Fig.  6a)  in 
which  has  been  put  100  c.c.  of  a  saturated  Ba(OH)2  solution. 
Carry  on  the  combustion  as  directed  above  and  when  the  CO2  has 
all  been  absorbed  filter  off  the  BaCO3  according  to  the  following 
directions.  Connect  the  absorption  bulb  as  shown  in  Fig.  6a. 
S  is  a  two-way  stop-cock  connected  with  suction.  The  bubble 
tube  (Meyer  tube)  is  fitted  with  two  rubber  stoppers  through 
which  short  pieces  of  glass  tubing  pass.  The  filter  C  contains  an 
ashless  filter  paper.  Insert  the  stopper  in  the  funnel  and  connect 
it  with  the  Meyer  tube  as  shown  in  the  drawing  and  apply  very 
gentle  suction.  When  necessary  open  P3  to  admit  air  back 
of  the  liquid  after  the  contents  of  the  tube  have  all  been  trans- 
ferred to  the  filter  bottle,  half  fill  the  large  bulb  nearest  B  with 
water  by  opening  the  pinch-cock  PI;  operate  the  stop-cock  S 
during  this  and  subsequent  operations  so  as  to  maintain  gentle 
suction.  Manipulate  the  tube  M  so  as  to  bring  the  wash  water 
into  contact  with  all  parts  of  the  interior  and  then  suck  out  the 
water  through  C ;  during  this  and  the  subsequent  washings  leave 
the  pinch-cock  P2  open.  After  eight  washings,  allowing  the  wash 
water  to  drain  off  thoroughly  each  time,  detach  M  and  complete 
the  washing  by  filling  C  to  the  top  with  water  free  from  carbonic 
acid,  sucking  dry  and  repeating  the  operation  once  more. 

Burn  off  the  filter  paper  at  a  dull  red  heat  and  weigh  the  BaC03. 
The  weight  multiplied  by  0.0608  gives  the  carbon. 

To  determine  the  carbon  by  titration  proceed  as  follows: 
Put  the  filter  paper  and  contents  in  a  small  flask,  add  an  excess 
of  N/10  HC1,  and  shake  the  flask  to  open  the  paper,  add  a  few 
drops  of  methyl  orange  solution  and  titrate  the  excess  of  acid 
with  N/10  NaOH.  The  difference  between  the  amounts  of 
N/10  acid  and  alkali  used  multiplied  by  0.0006  gram  gives  the 
carbon. 

See  page  57  for  direction  for  preparation  of  N/10  HC1  and 
N/10  NaOH. 

Notes. — One  hundred  and  fifty  cubic  centimeters  wash  water  will 
dissolve  about  0.0003  gram  BaCO3  =  0.000018  gram  carbon.  This 


CARBON  IN  PIG-IRON  AND  STEEL 


119 


would  be  negligible  for  present  purposes,  and  the  amount  dissolved  would 
be  really  less  than  this  because  of  the  repression  of  solubility  during  the 
first  washings  by  the  barium  hydroxide  still  present;  also  it  is  quite  pos- 
sible that  in  the  rapid  passage  through  the  filter  there  has  not  been 
sufficient  time  for  the  wash  water  to  become  saturated  with  barium 
carbonate. 

When  using  this  method  the  calcium  chloride  in  the  purifying  and 
absorbing  trains  is  not  necessary. 

When  working  with  steels  high  in  carbon  (above  1  per  cent.)  it  is 
advisable  not  to  use  more  than  1  gram,  in  order  that  filtration  may  be 
sufficiently  rapid.  For  very  accurate  work  the  Meyer  tubes  should  be 
washed  with  dilute  acid  before  beginning  work  each  day.  After  a  de- 


FIG.  6a. 

termination  is  finished,  the  Meyer  tube  should  be  completely  filled  two 
or  three  times  with  tap  water,  then  rinsed  with  distilled  water,  in  order 
to  remove  the  carbon  dioxide  liberated  when  dissolving  the  carbonate 
from  the  previous  determination. 

The  flask  containing  the  carbonate  should  be  very  thoroughly  agitated 
after  adding  the  acid,  since  the  carbonate  sometimes  dissolves  rather 
slowly  if  this  is  not  done;  this  is  particularly  the  case  if  it  has  packed 
much  during  filtration. 

The  rubber  tube  connecting  B  (see  Fig.  6a)  to  the  Meyer  tube  should 
be  washed  with  a  little  water  from  B,  before  beginning  determinations 
each  day. 

REFERENCE: 

CAIN,  J.  Ind.  Eng.  Chcrn.,  6,  465  (1914). 


120  METALLURGICAL  ANALYSIS 

Other  Dkect  Combustion  Processes. — For  alloys,  F.  Wust  mixes 
the  sample  with  five  times  its  weight  of  a  powdered  alloy  composed  of 
three  parts  of  tin  and  one  part  of  antimony  and  ignites  in  a  current  of 
oxygen  at  900°C.  Combustion  is  complete  in  10  minutes.  (Metal- 
lurgie,  VII,  page  321.) 

DeNolly  and  Queneau  burn  the  sample  of  steel  in  a  flask.  The 
sample  is  suspended  in  a  boat  in  the  flask  and  is  ignited  by  means  of 
electricity  applied  by  means  of  a  pair  of  electrodes  which  touch  the 
drillings.  A  current  of  oxygen  is  directed  on  the  drillings  until  com- 
bustion is  complete.  The  C02  is  absorbed  in  a  known  volume  of  stand- 
ard alkali  which  is  titrated  after  the  flask  is  cool.  Sulfur  is  said  not  to 
interfere.  Time  required  is  5  to  7  minutes.  (See  DENOLLY,  Chimiste, 
III,  26;  QUENEAU,  Met.  Chem.  Eng.,  IX,  441.) 

Mahler  and  Goutal  employ  a  bomb  and  burn  the  sample  in  oxygen 
at  eight  atmospheres  pressure.  The  drillings  are  fired  electrically  by 
means  of  a  fine  wire  as  in  calorimetry.  The  gas  is  passed  through 
Ba(OH)2  which  is  titrated  with  oxalic  acid.  (Compt.  rend.,  CLIII, 
549.) 

THE    DETERMINATION    OF   CARBON    IN    PIG-IRON    AND    STEEL 
INVOLVING  SEPARATION  OF  THE  CARBON  FROM  IRON 

When  a  sample  of  iron  is  dissolved  in  a  strong  solution  of  K2CuCl4 
all  of  the  carbon  in  the  sample  is  left  undissolved,  whether  it  be  present 
as  graphite,  combined  as  Fe3C  or  in  solid  solution  as  austenite.  The 
reactions  may  be  represented  as  follows: 

Fe+K2CuCl4  =  FeCl2+Cu+2KCl 
and 

Fe3C+3K2CuCl4  =  3FeCl2+3Cu+C+6KCl 

The  copper  then  redissolves  as  follows: 

K2CuCl4+Cu  =  2KCuCl2 

The  carbon  liberated  can  be  filtered  off  and  ignited  to  C02  by  either 
wet  or  dry  oxidation. 

It  is  essential  that  there  be  no  hydrogen  liberated  during  the  solu- 
tion of  the  iron  or  hydrocarbons  will  be  liberated  causing  loss  of  carbon. 
The  method  cannot  be  used  on  some  alloy  steels  or  ferro-alloys  because 
of  such  loss  of  carbon.  According  to  Moore  and  Bain  (J.  Soc.  Chem. 
Ind.,  XXVII,  845)  when  steel  is  dissolved  in  K2CuCl4,  there  is  a  slight 
loss  of  carbon  or  hydrocarbon.  The  higher  the  percentage  of  carbon 
in  solid  solution,  the  greater  seems  to  be  the  loss.  Thus  the  loss  is 


CARBON  IN  PIG-IRON  AND  STEEL  121 

greater  on  a  hardened  steel  than  on  the  same  steel  after  annealing. 
(DILNER,  J.  Iron  and  Steel  Inst.,  Vol.  XI,  1904,  p.  255.) 

The  carbonaceous  residue  often  contains  some  silica  and  phosphide 
of  iron  and  sulfide  of  copper.  Alloy  steels  may  also  give  a  residue  of 
tungsten,  chromium,  vanadium  and  molybdenum. 

The  KC1  serves  to  hold  the  cuprous  salt  in  solution  and  greatly  hastens 
the  action. 

This  solution  has  a  tendency  to  dissolve  organic  matter,  which  is  liable 
to  be  subsequently  precipitated  with  the  carbon  in  the  steel.  This  is 
especially  true  of  the  ammonium  salt,  it  being  very  difficult  to  obtain  it 
free  from  organic  matter  (derived  from  the  ammonium  salts  used  in 
its  manufacture).  The  salt  should  be  thoroughly  purified  by  re- 
crystallization.  The  potassium  salt  is  more  easily  obtained  free  from 
this  contamination  and  for  this  reason  is  to  be  preferred. 

A  large  excess  of  the  solution  is  required  to  prevent  separation  of 
metallic  copper  with  the  carbon. 

The  carbon  residue  retains  chlorides  very  difficult  to  wash  out, 
which  cause  trouble  in  the  subsequent  combustion.  If  any  metallic 
copper  is  precipitated  and  left  mixed  with  the  carbon,  it  will  form  basic 
subchlorides  nearly  insoluble  in  water.  The  spongy  carbon  is  best 
freed  from  chlorides  by  treating  with  dilute  HC1  and  then  washing  thor- 
oughly with  water. 

Instead  of  using  a  neutral  solution  of  potassium  cupric  chloride,  it 
is  usually  acidified  with  a  little  HC1.  The  presence  of  this  acid  will 
cause  no  loss  of  carbon,  provided  the  solution  is  kept  cool  while  the  iron 
is  dissolving. 

The  solution  after  having  been  used  can  be  regenerated  and  used 
again  by  passing  chlorine  gas  through  it  until  the  Cu2Cl2  is  changed  back 
again  to  CuCl2. 

REFERENCES: 

SARGENT,  J.  Am.  Chem.  Soc.,  1900,  p.  210. 

For  important  papers  on  the  carbon  determination  consult — 

Trans.  Am.  Inst.  Mining  Eng.,  XIX,  p.  614. 

J.  Anal,  and  App.  Chem.,  V,  p.  129. 

J.  Anal,  and  App.  Chem.,  V,  p.  122. 

J.  Am.  Chem.  Soc.,  1893,  p.  448,  526;  1895,  p.  873;  1898,  p.  243. 

Process.  Solution  of  the  Metal  and  Separation  of  the  Carbon. 
—Prepare  a  solution  of  the  double  chloride  of  copper  and  ammon- 
ium or  potassium.  Use  the  purest  crystallized  salt  obtainable. 
Dissolve  one  part  in  three  parts  of  pure  water,  free  from  grease 
or  organic  matter,  adding  about  5  per  cent,  of  concentrated 


122  METALLURGICAL  ANALYSIS 

HC1.  Let  the  liquid  settle,  decant  off  the  clear  solution,  and 
filter  any  turbid  portion  through  ignited  asbestos. 

Weigh  out  2  grams  of  pig-iron,  3  grams  of  high-carbon  steel  or 
5  grams  of  low-carbon  steel  or  wrought  iron.  Put  this  metal 
into  a  200  or  250  c.c.  beaker,  and  add  at  once  the  copper  solu- 
tion, using  50  c.c.  for  each  gram  of  the  sample  taken.  Stir  the 
liquid  continuously  until  the  iron  is  dissolved. 

If  an  air  blast  is  available,  this  stirring  can  be  accomplished 
by  blowing  air  through  the  liquid.  The  air  should  be  first 
passed  through  a  tube  filled  with  absorbent  cotton  to  filter  out 
any  dust. 

The  completion  of  the  reaction  is  recognized  by  the  residue 
becoming  light  and  "flotant."  At  first  more  or  less  copper  will 
separate,  but  continued  stirring  will  bring  it  into  solution. 

As  soon  as  all  the  separated  copper  has  disappeared,  let  settle 
a  few  minutes  if  necessary  and  decant  onto  an  asbestos  filter, 
disturbing  the  carbon  as  little  as  possible.  Add  10  c.c.  of  dilute 
HC1  (1  :1),  washing  down  the  sides  of  the  beaker  with  this  acid. 
Decant  this  through  the  filter.  When  the  liquid  has  all  run 
through  wash  out  the  beaker  and  transfer  all  adhering  carbon  to 
the  filter  with  the  dilute  HC1. 

Wash  the  carbon  on  the  filter  twice  with  acid.  Let  the  acid 
run  through  slowly  to  give  it  time  to  act.  Now  wash  with  water 
until  all  the  HC1  is  removed  and  the  filtrate  does  not  react  with 
AgN03. 

The  filtrate  will  be  dark  colored  at  first,  but  when  diluted  with 
the  HC1  and  water  will  become  lighter,  and  then  must  be  care- 
fully examined  to  see  that  no  particles  of  carbon  have  run  through 
the  filter. 

The  drillings  of  metal  must  be  free  from  all  grease  or  inter- 
mixed particles  of  wood,  straw  or  paper.  They  may  be  separated 
from  the  latter  by  a  magnet,  and  from  the  former  by  washing 
them  with  pure  ether,  and  drying.  Care  in  drilling  and  handling 
the  sample  will  render  this  treatment  unnecessary. 

The  weighing  out  of  pig-iron  for  this  carbon  determination 
is  a  matter  of  great  difficulty,  as  the  fine,  dusty  portion  is  usually 
higher  in  carbon  than  the  lumps.  A  method  proposed  by  Dr. 
Shinier  is  to  moisten  the  drillings  with  alcohol,  so  that  the  fine 
may  stick  to  the  coarse.  Then  take  a  portion  of  approximately 


CARBON  IN  PIG-IRON  AND  STEEL 


123 


T 


the  right  weight,  put  it  on  a  weighed  watch-glass,  dry  it  carefully 
and  reweigh.     Use  this  amount  in  the  determination. 

Preparation  of  the  Asbestos  Filter. — The  form  of  filter  shown 
in  Fig.  7  is  a  slight  modification  of  one  described  by  Professor 
Arnold  in  his  " Steel  Works  Analysis."  It  will  be  found  very 
convenient.  A  is  an  ordinary  heavy  glass  filtering  flask  such  as 
is  used  with  the  Bunsen  filter  pump.  It  should  have  a  capacity 
of  about  500  c.c.  B  is  a  piece  of  glass-tube  with  a  uniform  bore 
of  about  %  in.  and  about  9  in.  long.  This  passes  through  the 
rubber  stopper  in  the  neck  of  the  flask.  The  hole  in  this  stopper 
can  be  drilled  with  a  large  cork  borer  moistened  with  a  dilute 
solution  of  KOH.  Into  this  tube  a  second 
tube  C  is  inserted.  This  is  of  such  a  size  as 
to  just  slip  freely  through  the  larger  tube*. 
It  should  be  about  1  in.  longer  than  the  first 
tube  and  have  the  ends  ground  off  square. 
The  apparatus  should  be  so  arranged  that 
when  the  smaller  tube  rests  on  the  bottom 
of  the  flask  it  will  leave  about  two-thirds  of 
the  upper  tube  unoccupied.  Now  cut  a  disc 
of  platinum  foil  of  such  a  size  that  it  will 
freely  slip  into  the  larger  tube  and  rest  in 
place  on  the  end  of  the  inner  tube.  This 
platinum  disc  should  be  punched  full  of  holes 
with  a  needle.  It  is  advantageous  to  solder 
(with  a  bit  of  gold  and  a  blow  pipe),  a  piece 
of  stiff  platinum  wire,  E,  to  the  center  of  this 
disc  which  will  stick  down  into  the  lower  tube 
and  keep  the  disc  in  place.  This  wire  will  also  serve  as  a  con- 
venient handle  for  lifting  the  platinum  from  the  asbestos  mat 
after  it  is  removed  from  the  tube. 

Prepare  the  asbestos  for  the  felt  as  follows:  Select  long-fibered 
asbestos.  (Not  the  " cottony"  kind,  but  that  with  rather  stiff 
fibers.)  Cut  it  across  the  fiber  into  pieces  %Q  in.  long.  Ignite 
these  in  a  platinum  crucible  at  a  low  red  heat  for  at  least  30 
minutes.  When  cool  transfer  them  to  a  clean  porcelain  mortar 
and  "macerate"  them  to  a  pulp  with  strong  HC1.  Now  dilute 
the  paste  with  a  large  amount  of  water,  pour  into  a  beaker  and 
allow  the  mixture  to  settle  until  the  fibrous  mass  collects  at  the 


FIG.  7. 


124  METALLURGICAL  A. \ALYHIH 

bottom,  leaving  the  fine,  milky  silt  still  in  suspension.  Decant 
from  the  fibers  and  repeat  the  washing  until  the  wash  water  comes 
off  only  slightly  milky.  Asbestos  prepared  in  this  manner  makes 
a  felt  that  filters  very  rapidly.  If  the  fine  slimy  material  that  is 
formed  during  the  felting  is  left  in  the  mixture  it  will  clog  the 
filter  and  make  it  work  badly.  Preserve  the  felt  in  water  in  a 
stoppered  bottle.  To  form  the  filter  pour  enough  of  the  sus- 
pended felt  into  the  tube  to  form  a  layer  about  ^{Q  in.  thick  when 
drawn  down  by  suction  onto  the  platinum  disc  in  the  tube,  then 
attach  the  suction  pump.  Exactly  the  right  amount  must  be 
learned  by  experience.  But  when  right  it  will  .filter  rapidly  and 
yet  retain  the  finest  carbon. 

Draw  a  little  water  through  the  felt  to  wash  it  before  pouring 
on  the  carbon  solution.  After  the  carbon  is  filtered  and  washed 
take  the  stopper  with  the  tubes  out  of  the  bottle,  wash  off  the 
smaller  tube  and  then  push  it  carefully  through  the  larger  tube, 
forcing  out  from  below  the  disc  carrying  the  felt  and  carbon.  The 
felt  and  carbon  can  now  be  dropped  into  the  combustion  flask 
or  into  a  platinum  boat  for  combustion  in  oxygen.  With  a  little 
care  no  carbon  whatever  will  be  left  adhering  to  the  tube.  Should 
a  little  adhere  it  can  be  washed  off  into  the  flask  with  a  few  drops 
of  water  or  wiped  off  with  a  small  tuft  of  ignited  asbestos. 

The  boat  containing  the  carbon  is  now  analyzed  for  carbon  in 
the  furnace  as  previously  described  for  the  direct  combustion  of 
carbon  in  steel.  The  mass  should  be  dry  before  putting  it  in  the 
furnace. 

If  a  furnace  is  not  available,  the  following  wet  oxidation  method 
will  give  good  results. 

DETERMINATION  OF  THE  CARBON  BY  OXIDATION  WITH  CHROMIC 

ACID 

Carbon  in  any  form  is  rapidly  and  completely  oxidized  to  C02  when 
heated  with  chromic  acid  and  an  excess  of  sulfuric  acid. 

It  is  essential  that  the  sulfuric  acid  be  sufficiently  concentrated;  if 
too  dilute,  the  oxidation  will  be  incomplete  and  some  CO  will  be  formed 
which  will  escape  the  absorption  apparatus.  The  strength  of  acid  neces- 
sary depends  somewhat  on  the  condition  of  the  carbon,  as  the  amorphous 
carbon  from  steels  is  more  easily  oxidized  than  the  graphite  from  pig- 
iron.  In  no  case  should  the  mixture  contain  less  than  70  per  cent,  of 


CARBON  IN  PIG-IRON  AND  STEEL  125 

H2S04,  while  for  pig-irons  enough  should  be  present  to  give,  on  boiling, 
a  trace  of  white  fumes  of  H2S04.  If  not  present  in  large  amount  these 
white  fumes  will  be  arrested  in  the  purifying  train.  They  represent  only 
a  very  minute  quantity  by  weight.  When  the  acid  is  of  this  strength 
the  mixture  will  give  off  some  oxygen  gas  on  boiling. 

If  the  carbon  retains  chlorine  or  chlorides,  chlorine  and  chloro-chromic 
acid  gas  may  form,  escape  with  the  C02  and  be  absorbed  by  the  KOH, 
vitiating  the  results  unless  special  means  be  provided  for  absorbing 
them  in  the  purifying  train. 

The  HoS04  used  must  be  purified  from  all  organic  matter. 

Arrangement  of  the  Apparatus. — Fig.  8  shows  a  convenient 
form  of  train  for  the  use  of  students.  It  is  compact,  needs  no 
special  clamps,  and  can  be  taken  apart  and  set  away  in  a  labora- 
tory desk.  C  is  an  Erlenmeyer  flask  of  about  250  c.c.  capacity, 
fitted  with  a  two-hole  rubber  stopper;  into  one  hole  is  inserted  a 
bulb  funnel  tube  B,  having  a  glass  stop-cock,  and  into  the  other 
a  delivery  tube  M  for  the  gas. 

This  latter  should  be  of  rather  large  diameter  and  so  inclined 
that  everything  condensing  in  it  will  run  back  into  the  flask. 
It  is  a  good  plan  to  have  it  cooled  by  a  " water  jacket"  D,  con- 
sisting of  a  larger  tube  surrounding  the  smaller,  the  space  between 
the  two  being  filled  with  water. 

A  small  guard  tube  A,  filled  with  "soda  lime"  is  fitted  to  the 
top  of  the  funnel  tube. 

This  serves  to  remove  any  C02  from  the  air  drawn  into  the 
flask.  It  must  be  so  arranged  as  to  be  easily  connected  and  dis- 
connected. 

The  delivery  tube  is  connected  with  the  purifying  and  absorb- 
ing  apparatus  (or  " train")  arranged  in  the  order  shown. 

E  is  a  bottle  of  50  or  75  c.c.  capacity,  containing  about  30  c.c. 
of  a  solution  of  silver  arsenite  in  dilute  sulfuric  acid. 

This  serves  to  absorb  any  chlorine,  HC1  or  CrO2Cl2  in  the  gas. 
A  solution  of  silver  sulfate  may  be  used  instead,  but  this  does 
not  absorb  chlorine  nor  chromyl  chloride  and  is  usually  preceded 
by  a  bottle  containing  pyrogallic  acid  dissolved  in  a  solution  of 
potassium  oxalate  (LANGLEY).  When  using  the  arsenite  this 
is  unnecessary,  as  it  is  oxidized  to  arsenate  by  the  chlorine  and 
t  he  silver  precipitated  as  chloride. 

The  arsenite  solution  is  prepared  as  follows:  Dissolve  2  grams 


126 


METALLURGICAL  ANALYSIS 


of  pulverized  As203  in  the  smallest  possible  quantity  of  a  dilute 
solution  of  KOH.  Dilute  to  250  c.c.  and  add  dilute  H2SO4  till 
the  solution  is  neutral  to  litmus  paper.  Now  add  a  solution 
of  AgNO3  as  long  as  a  yellow  precipitate  forms,  carefully  keep- 
ing the  solution  neutral  by  adding  a  solution  of  KOH  drop  by 
drop  as  needed.  Stir  the  liquid  till  the  precipitate  clots,  let  it 
settle,  and  wash  it  thoroughly  by  decantation.  Finally  dissolve 
the  precipitate  in  a  slight  excess  of  dilute  H2SO4  (10  per  cent.). 


FIG.  8. 


Dilute  to  about  150  c.c.  and  filter  from  any  undissolved  AgCl. 
The  solution  keeps  well. 

The  silver  sulfate  is  made  by  dissolving  about  0.5  gram  of 
AgN03  in  a  little  water,  adding  1  c.c.  concentrated  H2S04, 
evaporating  till  the  HNO3  is  all  expelled,  cooling  and  diluting 
largely  with  water.  Ag2SO4  is  only  sparingly  soluble. 

F  is  a  bottle  containing  20  or  30  c.c.  of  pure  concentrated 
H2S04. 


CARBON  IN  PIG-IRON  AND  STEEL 


127 


This  takes  out  all  the  water  vapor  from  the  gas. 

G  is  a  U-tube  containing  granular  CaCl2.  Fill  about  an  inch 
of  the  tube,  on  the  side  next  to  the  H2S04  with  cotton  and 
moisten  the  top  of  this  with  a  drop  of  water  (BLAIR).  It  is 
shown  with  its  connecting  tube  in  Fig.  9,  C. 

The  object  of  this  CaCl2  is  to  absorb  water  and  to  bring  the  gas 
stream  entering  the  absorption  apparatus  (H  and  I)  into  the 
same  condition  as  to  moisture,  in  which  it  leaves  it.  H2S04 
will  dry  air  more  completely  than  CaCl2,  hence  if  the  gas  entered 
through  H2SO4  and  left  through  CaCl2  it  would  carry  out  more 
moisture  from  the  KOH  bulbs  than  it  brought  in  and  so  result 
in  loss  of  weight.  It  also  serves 
to  catch  any  white  fumes  of  H2SO4 
carried  over  by  the  gas. 

Dried  CaCl2  and  not  the  fused 
salt  should  be  used.  This  latter 
is  usually  alkaline  from  free  CaO 
and  will  absorb  some  C02. 

H  (Fig.  9)  shows  the  Liebig's 
potash  bulbs.  These  contain  a 
clear  solution  of  KOH  of  about 
sp.  gr.  1.27  (about  30  per  cent.). 

This  solution  absorbs  the  CO2 
but  not  completely  unless  the  gas 
stream  is  slow.  The  solution  gives 
up  a  little  water  to  the  gas  passing 

through.     If  made  stronger  than   directed   it   deposits   K2CO3 
which  may  clog  up  the  tube. 

As  caustic  potash  frequently  contains  nitrites  and  almost  in- 
variably traces  of  Fe(OH)2,  a  fresh  solution  will  absorb  oxygen, 
the  Fe(OH)2  gradually  precipitating  as  Fe(OH)3.  If  the  potash 
bulbs  are  filled  with  such  a  solution  they  will  frequently  continue 
to  increase  in  weight  for  some  time  if  air  alone  is  aspirated  through 
them.  This  troublesome  difficulty  may  be  entirely  overcome  if 
the  potash  solution  is  heated  to  boiling  before  using  and  a  solution 
of  potassium  permanganate  added  drop  by  drop  until  a  faint  per- 
sistent green  tint  is  produced.  The  liquid  is  then  allowed  to 
cool  and  settle,  and  the  clear  solution  decanted  for  use. 

I  is  a  small  U-tube,  with  the  limb  next  the  potash  bulbs  filled 


FIG.  9. 


128  METALLURGICAL  ANALYSIS 

with  granular  soda  lime.  This  should  not  be  too  dry.  The 
other  limb  is  filled  with  granular  CaCl2. 

This  tube  serves  to  catch  the  trace  of  CO2  escaping  the  bulbs, 
and  also  to  retain  the  moisture  carried  over  from  the  potash 
bulbs.  Soda  lime  is  a  more  rapid  and  complete  absorbent  for 
CO2  than  the  KOH  in  the  bulbs,  but  it  is  soon  exhausted.  By 
letting  the  bulbs  do  most  of  the  work  and  only  using  the  soda 
lime  as  a  guard,  it  lasts  for  many  operations  and  retains  every 
trace  of  the  CO2.  The  potash  bulbs  and  the  soda  lime — calcium 
chloride — tube  are  the  parts  of  the  train  to  be  weighed.  They 
may  be  weighed  separately  or  together.  In  the  latter  case  they 
should  be  permanently  combined  into  one  piece  as  shown  in  Fig. 
9,  A  and  B,  a  very  convenient  arrangement.  The  ends  of  the 
tubes  are  bent  over,  as  shown  at  F  and  G  (Fig.  9).  When  con- 
nected up,  the  tube  and  bulbs  should  so  support  each  .other  as  to 
stand  upright  safely. 

J  is  a  U-tube  similar  to  the  last,  but  larger,  having  the  limb 
next  to  I  filled  with  CaCl2,  and  the  other  with  granular  soda  lime. 

This  serves  as  a  guard  tube  to  prevent  moisture  or  C02  working 
back  into  the  absorption  apparatus  from  the  aspirator.  It  can 
be  used  almost  indefinitely  without  becoming  exhausted. 

K  is  an  aspirator  for  sucking  air  slowly  through  the  apparatus. 

This  must  be  arranged  so  that  it  can  be  easily  attached  and 
detached.  It  can  be  made  from  a  5  pint  acid  bottle  by  boring  a 
hole  near  the  bottom  with  a  pointed  file  dipped  in  turpentine, 
fitting  a  glass  tube  in  this  by  a  rubber  ring  and  then  attaching 
to  this  a  rubber  tube  and  pinch-cock. 

Notes  on  the  above  Apparatus. — It  is  essential  that  none  of  the 
chromic  acid  solution  come  into  contact  with  the  rubber  stopper  or 
connections,  as  it  would,  of  course,  form  C02.  For  similar  reasons  it  is 
necessary  that  the  glass  stop-cock  in  the  funnel  tube  be  free  from  grease 
of  any  sort. 

A  flask  provided  with  a  ground  glass  cap,  into  which  the  tubes  are 
fused,  may  be  substituted  for  the  rubber  stoppered  flask  as  described. 

Liquids  always  absorb  some  C02,  hence  the  volume  of  all  absorbing 
liquids  used  in  the  purifying  train  must  be  small.  The  C02  absorbed  is, 
however,  given  up  again  to  a  current  of  air  passed  through  them  for  some 
time. 


CARBON  IN  PIG-IRON  AND  STEEL  129 

Setting  up  and  Testing  the  Apparatus. — The  connection  tubes 
are  united  by  short  rubber  tubes.  These  must  be  carefully  tied 
with  thread  or  wire  or  rubber  band,  as  it  is  essential  that  the 
whole  apparatus  be  air  tight.  Rubber  stoppers  are,  of  course, 
the  best,  but  good  ordinary  corks  can  be  used  if  rolled  soft  and 
carefully  bored  and  fitted.  Sealing  wax  should  not  be  used  on 
these  corks  to  make  the  joints  tight,  as  it  is  liable  to  crack  and 
leak  unexpectedly.  The  potash  bulbs  and  U-tube  may  be 
" capped"  when  disconnected,  by  short  rubber  tubes  closed  with 
bits  of  glass  rod.  These  caps  must  always  be  removed  for  a 
moment  and  then  replaced  just  before  weighing,  that  the  air 
pressure  inside  and  outside  the  bulb  may  become  equal. 

If  the  ends  of  the  glass  tubes  are  heated  until  they  draw  to- 
gether leaving  only  a  small  opening  the  size  of  a  knitting  needle, 
the  rubber  "caps"  need  not  be  used,  provided  the  weighing  is 
promptly  done,  as  these  small  holes  will  not  admit  of  any  notice- 
able diffusion  of  moisture  into  the  bulbs. 

It  is  desirable  to  pass  some  CO2  through  the  apparatus  after 
first  setting  it  up,  in  order  to  saturate  any  alkalirie  material 
present  in  the  CaCl2,  etc.  When  this  is  done  the  weighed  part 
of  the  train  is,  of  course,  omitted.  Connect  up  the  train,  leaving 
out  the  parts  H,  I  and  J.  Put  a  little  marble  in  the  flask,  and 
add  a  little  dilute  H2SO4  to  generate  a  slow  stream  of  CO2.  Let 
this  run  through  the  portion  of  the  train  remaining  for  about 
30  minutes.  Disconnect  and  wash  out  the  flask,  replace  it,  and 
then  aspirate  air  until  3  or  4  liters  have  been  slowly  drawn 
through  the  apparatus. 

Now  connect  up  the  whole  train  and  attach  the  aspirator. 
Close  the  stop-cock  in  the  funnel  tube  of  the  flask  and  see  if  all 
connections  are  tight.  This  is  shown  if  the  water  entirely  stops 
running  from  the  aspirator.  Let  in  air  cautiously  by  opening 
the  stop-cock  in  the  funnel  tube.  Attach  the  soda  lime  guard- 
tube  to  the  funnel  tube  and  aspirate  1  or  2  liters  of  air  carefully 
(not  over  four  or  five  bubbles  a  second).  Disconnect  the  bulbs 
and  the  U-tube,  cap  them,  and  wipe  them  carefully.  Set  them 
in  or  near  the  balance  case  until  they  attain  its  temperature 
(10  or  20  minutes).  Uncap  them  a  moment,  replace  the  caps  and 
then  carefully  weigh  them.  Replace  them  in  the  train  and  aspir- 
ate 1500  c.c.  more  of  air,  detach  and  reweigh  them.  The  KOH 


130  METALLURGICAL  ANALYSIS 

bulb  will  lose  (due  to  giving  up  moisture)  and  the  U-tube  will 
gain  weight.  The  loss  in  one  must  equal  the  gain  in  the  other. 
The  total  weight  of  the  absorption  apparatus  must  not  change 
more  than  J^  mg. 

Treatment  of  the  Carbon  Residue  from  the  Iron. — Transfer 
this  to  the  flask  C,  using  as  little  water  as  is  necessary  to  wash  out 
the  filter  tube.  The  total  amount  of  liquid  in  the  flask  must  not 
exceed  20  c.c.  Now  dissolve  4  grams  of  chromic  acid  in  4  c.c.  of 
water,  and  pour  it  into  the  flask  through  the  funnel  tube,  follow- 
ing it  with  2  or  3  c.c.  of  water  to  wash  out  the  tube.  Now  put 
into  the  bulb  of  the  funnel  a  quantity  of  concentrated  H2SO4, 
equal  to  about  two  and  a  half  or  three  times  the  volume  of  the 
liquid  in  the  flask. 

This  volume  can  be  estimated  by  pouring  water  into  a  second 
similar  flask  until  it  appears  to  contain  the  same  amount  of  liquid 
as  the  first  and  then  measuring  the  quantity  used. 

The  acid  used  should  be  purified  from  any  trace  of  organic 
matter  that  it  may  contain,  by  adding  a  little  chromic  acid  to  a 
quantity  of  it  and  then  heating  it  to  about  200°C.  for  a  few  min- 
utes. Let  it  stand  till  cool  before  using. 

Now  open  the  stop-cock  and  run  the  acid  slowly  into  the  flask, 
being  careful  to  avoid  too  violent  action.  When  the  acid  is  all 
in,  shake  the  flask  carefully  to  mix  the  contents. 

The  evolution  of  C02  will  begin  at  once.  Finally  heat  carefully 
to  boiling,  so  regulating  the  heat  that  the  evolution  of  the  gas 
does  not  take  place  too  rapidly.  The  gas  should  not  pass  through 
the  potash  bulbs  faster  than  two  or  three  bubbles  per  second. 
The  boiling  should  be  continued  for  two  or  three  minutes.  At 
the  end  of  this  time  but  little  gas  should  be  coming  over  through 
the  bottles;  but  as  some  oxygen  is  likely  to  be  given  off  by  the 
chromic  acid  mixture,  it  is  usually  not  possible  to  continue  boil- 
ing till  the  evolution  of  gas  ceases.  Now  withdraw  the  lamp 
and  immediately  open  the  stop-cock  of  the  funnel  tube  to  admit 
air  and  prevent  back  suction.  Connect  the  funnel  tube  with 
the  soda-lime  guard  tube,  and  let  the  apparatus  cool  a  few  min- 
utes. Then  aspirate  carefully  until  a  volume  of  air  has  been 
drawn  through  equal  to  seven  or  eight  times  the  capacity  of  the 
apparatus. 

Detach  the  absorption  apparatus  and  weigh  it.     The  total 


CARBON  IN  PIG-IRON  AND  STEEL  131 

gain  in  weight  will  be  the  amount  of  C02  formed,  and  this  multi- 
plied by  0.2727  gives  the  amount  of  carbon  in  the  sample  taken. 

The  greatest  care  and  "handiness"  are  necessary,  but  with 
skill  duplicates  should  agree  within  0.01  per  cent. 

The  solution  should  not  be  brought  to  the  boiling-point  too 
rapidly.  By  raising  the  temperature  slowly  time  is  given  for  the 
reaction  and  most  of  the  carbon  will  be  oxidized  before  the  liquid 
begins  to  boil.  If  much  unoxidized  carbon  is  present  in  the  boil- 
ing liquid,  particles  of  it  are  likely  to  be  carried  up  onto  the  sides 
of  the  flask  where  they  will  adhere  and  so  escape  oxidation. 

If  white  fumes  form  toward  the  end  of  the  boiling,  let  the  flask 
cool  until  they  disappear  before  aspirating. 

The  foregoing  method  of  determining  carbon  by  combustion 
with  chromic  acid  is  very  accurate  if  conducted  carefully. 
It  has  the  advantage  of  demanding  no  special  or  expensive 
apparatus. 

THE  DETERMINATION  OF  CARBON  IN  STEEL  BY  COLOR 

This  method  is  in  general  use  in  steel  works.  It  depends  upon  the 
fact  that  when  steel  is  dissolved  in  dilute  HNOs  a  brown  compound  con- 
taining the  carbon  forms.  This  goes  into  solution,  on  boiling,  coloring 
the  liquid  more  deeply  as  the  percentage  of  carbon  is  higher.  Pure  iron 
dissolves  in  HNOs,  sp.  gr.  1.2,  giving  a  nearly  colorless  solution,  and 
from  which  every  trace  of  color  is  removed  by  moderate  dilution. 

The  color  produced  by  the  carbonaceous  matter  is  rapidly  altered  by 
light.  Its  depth  depends  somewhat  on  the  mode  of  solution,  the  concen- 
tration of  the  acid  and  the  kind  of  steel,  hence  the  process  must  be  con- 
ducted strictly  according  to  rule  to  get  concordant  results. 

There  is  required :  First,  a  standard  steel,  which  must  be  of  exactly  the 
same  kind  as  that  to  be  tested,  and  also  similar  in  its  composition  and  of 
approximately  the  same  carbon  percentage.  The  carbon  in  this  must 
have  been  accurately  determined  gravimetrically.  Second,  nitric  acid 
of  sp.  gr.  1.2,  perfectly  free  from  chlorine,  the  least  trace  of  which  will 
seriously  alter  the  color  of  the  iron  solution,  making  it  more  yellow. 
The  above  strength  corresponds  to  one  volume  of  concentrated  acid  to 
one  volume  of  water.  Third,  comparison  tubes  of  clear  white  glass, 
graduated  in  ^o  c.c.,  and  of  exactly  equal  diameters. 

For  comparing  the  colors  an  arrangement  such  as  is  shown  in  Fig.  10 
is  convenient.  It  consists  of  a  wooden  box  open  at  one  end  and  closed  by 
a  sheet  of  ground  glass  at  the  other.  The  glass  is  covered  with  black 


132 


METALLURGICAL  ANALYSIS 


paper,  except  the  two  slits,  A,  before  which  the  tubes  are  placed  and 
compared  by  the  observer,  who  looks  into  the  large  end  of  the  box.  The 
tubes  are  carried  by  a  little  rack,  B,  which  can  be  revolved  by  turning  the 
knob,  C,  and  the  tubes  thus  reversed  without  taking  them  out  of  the  box. 
This  reversal  of  the  tubes  is  important,  as  the  eye  will  usually  see  the 
right-hand  tube  darker.  In  the  absence  of  such  a  " camera"  a  piece 
of  wet  paper  on  a  window  makes  a  good  temporary  background.  Many 
kinds  of  colorimeters  are  on  the  market. 

If  the  steel  contains  much  sulfur  the  solution  will  be  slightly  turbid 
from  free  S.  Comparison  is  difficult  in  this  case. 

The  volume  of  acid  used  should  bear  some  relation  to  the  percentage 
of  carbon  present.  The  amount  of  metal  taken  must  be  increased  when 

the  carbon  is  low.  It  is  essen- 
tial that  both  standard  and 
sample  be  treated  exactly  alike, 
as  to  the  amount  of  sample  taken, 
time  of  heating  and  volume  of 
acid.  It  is  especially  important 
that  the  standard  and  the  sample 
should  have  undergone  the  same 
"heat  treatment"  in  their  manu- 
facture. Only  the  combined  car- 
bon is  determined  by  the  color 
method,  any  free  carbon  present 
not  affecting  the  color. 

FIG.  10.  Process  of  Analysis. — Weigh 

0.2  gram  of  the  steel  and  of  the 

standard,  each  into  a  6  in.  test  tube.  Add  to  each  tube  a  meas- 
ured volume  of  cold  HNO3  sp.  gr.  1.2,  using  the  following  amount: 
For  steels  with  not  over  %{y  per  cent,  carbon,  4  c.c. ;  from  %o  to 
jKo  Per  cent.  6  c.c.;  from  ^{Q  to  1  per  cent.,  8  c.c.;  and  over  1  per 
cent.,  10  c.c. 

Stand  the  tubes  in  cold  water  till  violent  action  ceases.  Then 
set  them  in  boiling  water  and  heat  until  the  solution  is  perfectly 
clear  and  no  more  fine  bubbles  of  gas  appear.  Keep  the  mouths 
of  the  test-tubes  closed  loosely  by  little  glass  bulbs  or  balls  to 
prevent  drying  of  the  iron  salts  on  the  sides  of  the  tubes.  The 
time  required  will  be  from  15  to  30  minutes,  according  to  the 
percentage  of  carbon  in  the  steel.  Now  cool  the  tubes  in  water. 
Add  an  equal  volume  of  water  to  each  and  pour  into  the  com- 
parison tubes.  Dilute  carefully  until  the  colors  match.  The 


CARBON  IN  PIG-IRON  AND  STEEL  133 

percentages  of  the  carbon  will  be  to  each  other  as  the  volumes  of 
the  liquids  in  the  tubes. 

Where  a  number  of  steels  are  to  be  tested  at  once  it  is  conven- 
ient to  dilute  the  standard  until  each  cubic  centimeter  repre- 
sents some  definite  percentage  of  carbon,  and  then  match  it  with 
the  others,  so  that  the  readings  in  cubic  centimeters  can  be  readily 
converted  to  per  cents.  For  example,  if  the  standard  contained 
0.38  per  cent.  C,  dilute  it  to  19  c.c.,  then  if  a  comparison  showed 
the  unknown  steel  to  read  16  c.c.  it  would  obviously  contain 
0.32  per  cent,  carbon. 

Where  the  color  carbon  process  is  used  on  steels  of  compara- 
tively uniform  contents,  it  is  usual  to  take  10  c.c.  of  acid  and  then 
enough  of  the  sample  to  give  a  sufficiently  marked  color  with 
this  amount;  for  example,  0.5  gram  of  steel  and  10  c.c.  of  acid. 
In  the  case  of  very  low  carbon  steel  (under  0.2  per  cent.)  1  gram 
of  steel  may  be  dissolved  in  20  c.c.  of  acid. 

Notes  on  the  Process. — The  color  process  can  be  applied  to  pig-iron 
and  gives  an  approximate  determination  of  its  combined  carbon.  In 
this  case  a  solution  of  the  sample  and  of  the  standard  must  each  be 
filtered  through  a  small  filter  and  the  solutions  compared.  Filters  of  the 
same  size  and  a  pig-iron  standard  must  be  used. 

The  use  of  permanent  standard  colors,  either  organic  or  inorganic, 
such  as  the  mixed  chlorides  of  iron,  copper  and  cobalt,  has  been  tried. 
This  is  not  advisable  as  it  does  not  provide  for  the  variations  in  color  due 
to  slight  differences  in  the  treatment,  as  well  as  does  the  treatment  of 
standard  and  sample  together.  For  these  methods  see  Trans.  Am.  Inst. 
Mining  Eng.,  I,  p.  240,  and  XVI,  p.  111. 

For  very  low  carbon  steels  the  color  is  faint  and  uncertain.  An  alka- 
line method  has  been  used  on  such  metals.  (See  STEAD,  J.  Iron  and 
Steel  Inst.,  1883,  No.  1,  p.  213.) 

THE  DETERMINATION  OF  THE  GRAPHITE  IN  PIG-IRON 

When  pig-iron  is  boiled  with  HC1  or  dilute  HN03  the  combined  carbon 
is  converted  into  solid,  liquid,  or  gaseous  hydrocarbons  or  nitro  com- 
pounds; while  the  graphite  is  all  left  insoluble.  The  non-volatile  hydro- 
carbons are  soluble  either  in  alkalies,  in  alcohol,  or  in  ether.  The 
graphite  or  uncornbined  carbon  is  not  acted  upon  by  any  of  these  re- 
agents but  remains  in  the  residue  as  a  black  mass.  The  residue  may  also 
contain  hydra  tod  silica  and  frequently  titanium  carbide  and  free  sulfur. 


134  METALLURGICAL  ANALYSIS 

The  silica  holds  water  tenaciously  and  cannot  be  thoroughly  dehydrated 
below  a  red  heat.  Titanium  carbide  is  decomposed  by  HN03  but  not  by 
HC1;  while  sulfur  is  separated  by  dilute  HN03  but  not  by  HC1.  Graph- 
ite is  not  at  all  oxidized  by  HN03,  sp.  gr.  1.2.  The  use  of  nitric  acid  is 
preferable  with  gray  irons  low  in  combined  carbon,  while  HC1  is  better 
for  white  iron  high  in  combined  carbon  and  for  ferrosilicons  as  these  only 
dissolve  with  difficulty  in  HN03.  The  carbon  in  the  residue  can  only  be 
accurately  determined  by  combustion. 

REFERENCES: 

SHIMEK,  J.  Am.  Chem.  Soc.,  Vol.  XVII,  p.  873. 
DROWN,  Trans.  Am.  Inst.  Mining  Eng.,  Vol.  Ill,  p.  41. 

Process  of  Analysis. — Treat  2  grams  of  drillings  in  a  beaker  with 
50  c.c.  of  HC1,  sp.  gr.  1.12.  Cover  and  boil  briskly  for  30  minutes. 
Dilute,  filter  on  an  asbestos  filter  and  wash  with  hot  water  until 
all  iron  salts  are  removed.  Then  pour  on  a  little  HC1  and  wash 
again  with  water.  Now  wash  the  residue  with  a  30  per  cent,  solu- 
tion of  caustic  soda,  then  with  water,  then  with  alcohol,  then  with 
ether,  and  finally  with  cold  water,  then  hot  water  till  every  trace 
of  ether  is  extracted.  Now  transfer  to  the  carbon  apparatus 
and  determine  the  carbon  with  chromic  acid  and  sulfuric  acid, 
or  by  combustion  in  oxygen. 

This  complicated  washing  is  required  to  remove  the  solid  and  liquid 
hydrocarbons  which  are  likely  to  form  and  are  insoluble  in  water  alone. 

The  ether  must  be  followed  by  cold  water;  if  hot  water  were  added  at 
once,  it  would  make  the  ether  boil  and  might  throw  the  carbon  out  of  the 
filter  tube.  Nitric  acid  of  sp.  gr.  1.135  can  be  substituted  for  HC1  with 
such  irons  as  are  readily  dissolved  by  it.  If  a  little  HF  is  added  to  the 
solution  after  the  metal  is  dissolved  it  will  frequently  greatly  facilitate 
the  nitration  by  preventing  the  separation  of  silica  in  a  gelatinous  form. 
By  using  a  sufficient  quantity  of  acid  of  the  right  specific  gravity,  most 
of  the  silica  will  usually  remain  in  solution. 

DETERMINATION  OF  THE  GRAPHITE  BY  DIRECT  WEIGHING 

This  method  gives  satisfactory  results  on  many  irons.  It  is  quite 
generally  used  as  a  rapid  method.  It  should  be  checked  by  the  combus- 
tion method  when  applied  to  kinds  of  iron  not  previously  tested. 

The  residue  is  dried  at  100°C.  and  then  burned  and  the  loss  of  weight 
assumed  to  be  carbon.  Any  sulphur  or  water  that  the  residue  contains 
will,  of  course,  be  rated  as  carbon. 


CARBON  IN  PIG-IRON  AND  STEEL  135 

Process. — \\feigh  out  2  grams  of  the  drillings  into  a  250  c.c. 
beaker.  Add  100  c.c.  of  HC1,  sp.  gr.  1.1,  or  of  HNO3,  sp.  gr. 
1.135.  Boil  gently  till  all  action  ceases.  Keep  the  beaker 
covered  to  prevent  evaporation  and  concentration  of  the  solution 
which  may  cause  the  separation  of  silica.  Finally  add  three  or 
four  drops  of  HF  and  boil  again.  Prepare  a  Gooch  perforated 
crucible  as  follows:  First,  heat,  cool  and  weigh  it;  second,  fit 
into  the  bottom  of  the  crucible  a  disc  of  ashless  filter  paper  and 
dry  the  paper  and  crucible  at  100°  for  20  minutes  and  weigh  again. 
Filter  the  solution  through  this  crucible  in  the  ordinary  way, 
transferring  the  residue  with  cold  water.  Then  wash  the  residue 
with  hot  dilute  HC1,  then  with  hot  water,  and  then  with  a  5  per 
cent,  solution  of  NH4OH.  When  the  filtrate  runs  through 
colorless  finally  wash  with  a  mixture  of  equal  parts  of  alcohol 
and  ether.  Now  dry  the  crucible  and  contents  at  100°C.  to 
constant  weight  which  will  take  from  10  to  20  minutes.  Now  set 
the  crucible  over  a  Bunsen  burner  flame  and  burn  off  the  residue. 
When  all  the  carbon  has  burned  away,  weigh  the  crucible  again. 

By  subtracting  the  weight  of  the  crucible  with  the  filter  paper, 
from  the  weight  of  the  crucible  plus  the  filter  paper  plus  the 
residue,  the  weight  of  the  residue  is  obtained.  Subtracting  the 
weight  of  the  empty  crucible  from  the  final  weight  of  the  crucible 
plus  the  incombustible  portion  of  the  residue,  gives  the  silica 
and  other  mineral  matter  with  the  carbon.  Subtracting  this 
remainder  from  the  total  weight  of  the  carbonaceous  residue 
gives  the  weight  of  the  graphite.  A  still  better  way  is  to  use  an 
asbestos  mat  in  the  Gooch  crucible. 

Instead  of  using  a  Gooch  crucible,  two  small  tared  filters  can 
be  taken  and  the  residue  then  burned  out  in  an  ordinary  crucible, 
but  this  is  not  nearly  so  convenient. 

The  above  method  is  essentially  that  given  by  A.  B.  Harrison  in 
"  Methods  of  Iron  Analysis  used  around  Pittsburg,"  2nd  edition,  p.  85. 

REFERENCES: 

For  variations  of  the  method  and  discussion  of  the  results  consult : 
DAUGHERTY,  Chem.  News,  Sept.  8,  1899. 
CROBAUGH,  J.  Am.  Chem.  Soc.,  1894,  p.  104. 
AUCHY,  J.  Am.  Chem.  Soc.,  1900,  p.  47. 


CHAPTER  IX 

THE   DETERMINATION    OF   NICKEL   AND    COBALT   IN 

STEEL 

The  method  for  nickel  here  given  is  that  of  Moore  modified  by  John- 
son. It  is  very  rapid  and  accurate  and  no  elements  interfere  except 
copper  and  cobalt  which  are  usually  present  in  steel  in  very  small 
amounts.  The  copper  reacts  like  nickel  and  if  present  in  more  than 
traces  must  be  separated  as  directed  on  page  173. 

The  method  depends  upon  the  following  reaction  : 


This  reaction  takes  place  in  a  solution  slightly  alkaline(with  ammonia) 
and  a  very  large  amount  of  iron  may  be  present  without  interfering  if 
before  making  alkaline  a  large  amount  of  citric  acid  is  added.  The 
citric  acid  which  has  the  formula 

CH2COOH 

I 
CH—  C—  COOH 

CH2COOH 

combines  with  the  iron  to  form  un-ionized  iron  citrate  which  does  not 
allow  the  iron  to  precipitate  when  the  ammonia  is  added. 

The  end  point  of  the  reaction  between  the  nickel  and  the  cyanide  is 
shown  by  the  disappearance  of  a  turbidity  due  to  the  presence  of  silver 
iodide.  The  reaction  is: 

AgI+2KCN  =  KAg(CN)2+KI. 

Process  of  Analysis.  —  Dissolve  1  gram  of  steel  drillings  in  a 
150  c.c.  beaker  with  20  c.c.  of  1:1  hydrochloric  acid.  When 
action  ceases  add  10  c.c.  of  1  :1  nitric  acid. 

Reduce  the  volume  to  15  c.c.,  remove  the  beaker  from  the  heat 
and  pour  into  it  8  c.c.  of  sulfuric  acid  diluted  with  25  c.c.  of  water. 
Transfer  the  contents  of  the  beaker  to  a  400  c.c.  beaker  contain- 
ing 12  grams  of  powdered  citric  acid  and  stir  until  it  is  all  dis- 

136 


THE  DETERMINATION  OF  NICKEL  IN  STEEL          137 

solved.  'Make  the  solution  faintly  but  distinctly  alkaline  with 
1  : 1  NEUOH.  Do  not  add  much  excess  as  it  causes  low  results. 
Cool  the  solution  and  dilute  to  about  300  c.c.  If  it  is  turbid, 
filter  it. 

Add  to  the  cold  solution  2  c.c.  of  a  20  per  cent,  solution  of 
potassium  iodide  and  then  run  in  from  a  burette  a  standard  solu- 
tion of  silver  nitrate  with  stirring  until  a  distinct  turbidity  due 
to  silver  iodide  is  produced.  Then  titrate  with  the  standard 
cyanide.  Run  in  the  cyanide  with  constant  stirring  until  the 
turbidity  just  disappears.  The  cyanide  first  reacts  with  the 
nickel  then  attacks  the  iodide.  If  it  is  thought  that  the  end  point 
is  passed  add  another  measured  amount  of  silver  nitrate  until  a 
turbidity  is  formed  and  again  titrate  with  the  cyanide  until  the 
turbidity  just  disappears.  It  is  best  to  have  another  beaker  con- 
taining a  solution  to  be  titrated  to  which  no  silver  nitrate  has 
been  added  sitting  beside  the  one  being  titrated  so  as  to  have  a 
clear  solution  of  the  same  color  to  compare  with.  If  the  citric 
acid  was  dirty,  the  solutions  will  be  cloudy  and  should  be  filtered 
before  the  silver  nitrate  is  added. 

Standardization  of  the  Solutions. — Dissolve  about  5  grams  of 
KCN  and  5  grams  of  KOH  in  water  and  dilute  to  1  liter.  The 
KOH  makes  the  KCN  solution  keep  better.  Also  dissolve  2.925 
grams  of  AgNO3  in  water  and  dilute  to  500  c.c.  One  cubic  centi- 
meter of  each  will  be  equal  to  about  0.001  gram  of  nickel.  To 
standardize  them,  weigh  out  1  gram  of  nickel-free  steel  and  add 
0.3370  grams  of  NiSO^NH^SC^GHzO,  which  contains  14.85  per 
cent,  of  nickel,  and  treat  just  as  above  directed  for  a  nickel  steel 
up  to  the  point  of  titration.  Make  the  titration  carefully  until 
the  turbidity  just  disappears.  Now  add  10  c.c.  of  the  cyanide  in 
excess  and  titrate  with  the  silver  nitrate  until  a  turbidity  just 
appears.  This  second  titration  gives  the  relation,  between  the 
silver  nitrate  solution  and  the  cyanide  solution.  For  example, 
suppose  that  in  the  first  place  0.5  c.c.  of  silver  solution  were  added 
and  50.5  c.c.  of  cyanide  were  used.  Then  suppos.e  that  it  took 
10.8  c.c.  of  silver  nitrate  solution  to  produce  a  turbidity  after 
the  10  c.c.  of  extra  cyanide  was  added.  The  cyanide  required  to 

titrate    the    nickel    would    be    50.5  -  0.5  X  ,     '    =  50.04    c.c. 

lU.o 

Since  the  amount  of  nickel  present  was  0.3370  X  0.1485  or  0.050 


138  METALLURGICAL  ANALYSIS 

gram,  the  strength  of  the  cyanide  is  0.050  +  50.04  =  0.0009992 
gram  Ni  per  cubic  centimeter. 

Notes  on  the  Process. — The  presence  of  sulfates  is  necessary  to  obtain 
a  sharp  end  reaction.  Silver  iodide  is  soluble  in  a  large  excess  of  NH4OH, 
so  care  should  be  taken  to  have  the  solution  only  slightly  alkaline  with 
NH4OH.  But  it  must  be  alkaline. 

If  the  titrated  solutions  are  allowed  to  remain  in  the  open  beakers  for 
some  time  a  white  film  forms  on  the  surface  but  no  account  is  to  be  taken 
of  it. 

When  chromium  is  present,  proceed  exactly  as  described  above  except 
to  add  24  grams  of  citric  acid.  Instead  of  using  so  much  citric  acid  some 
chemists  use  citric  acid  and  sodium  pyrophosphate. 

The  silver  nitrate  solution  used  should  not  be  stronger  than  that  indi- 
cated above,  for  when  a  strong  silver  solution  is  used,  the  silver  iodide 
instead  of  forming  a  turbid  solution  settles  out  as  a  curdy  precipitate 
which  does  not  readily  react  with  the  cyanide.  If  a  ferro-nickel  is  be- 
ing analyzed  a  stronger  solution  of  KCN  should  be  used. 

Such  elements  as  vanadium,  chromium,  tungsten,  molybdenum  or 
manganese  do  not  interfere  even  when  present  in  large  amounts  in  the 
sample. 

REFERENCES: 

JOHNSON,  "Chemical  Analysis  of  Special  Steels,  Alloys  and  Graph- 
ites." 

GROSSMAN,  Chem.  Ztg.,  XXXIV,  673. 
JAMIESON,  J.  Am.  Chem.  Soc.,  XXXII,  757. 
BOYLE,  Chem.  Eng.,  XIV,  288. 

THE    DlMETHYLGLYOXIME    METHOD    FOR    NlCKEL 

This  is  a  very  accurate  and  fairly  rapid  method.  Copper  and  cobalt  if 
present  do  not  interfere  and  for  this  reason  steels  containing  more  than 
traces  of  copper  or  cobalt  should  be  analyzed  by  this  method.  In  cases 
of  dispute  umpire  analyses  should  be  made  in  this  way. 

From  faintly  ammoniacal  solution  dimethylglyoxime  precipitates 
nickel  promptly  and  completely  as  a  voluminous  red  compound,  nickel 
dimethylglyoxime,  which  is  soluble  in  acid  solutions.  The  precipitate 
has  the  composition  (CH3)2C2(NOH)2Ni(CH3)2C2(NO)2  and  when  dried 
at  115°C.  contains  20.32  per  cent,  nickel. 

For  use  the  dimethylglyoxime  (CH3CNOHCNOHCH3)  is  dissolved  in 
alcohol,  1  gram  to  100  c.c.  Since  the  precipitate  is  distinctly  soluble  in 
a  solution  containing  more  than  50  per  cent,  of  alcohol  the  volume  of  the 


THE  DETERMINATION  OF  NICKEL  IN  STEEL  139 

solution  to  which  the  alcoholic  dimethylglyoxime  is  added  should  be 
greater  than  that  of  the  alcoholic  solution. 

Method  of  Analysis. — Treat  the  sample  exactly  as  was  directed 
for  the  cyanide  determination  of  nickel  until  the  ammonia  is 
added  to  the  solution  containing  citric  acid.  As  soon  as  the 
solution  becomes  alkaline  add  acetic  acid  until  it  is  acid  and  then 
heat  to  boiling.  Now  add  about  20  c.c.  of  the  dimethylglyoxime 
solution  or  five  times  as  much  dimethylglyoxime  as  there  is 
nickel  present.  Then  add  ammonia  until  the  solution  smells 
slightly  of  ammonia  or  reacts  alkaline.  While  still  hot  filter  on 
a  weighed  Gooch  crucible,  wash  well,  dry  at  110-120°C.  for 
45  minutes  and  weigh.  Multiply  the  weight  by  0.2032  to  get  the 
weight  of  the  nickel. 

Notes  on  the  Process. — The  nickel  dimethylglyoxime  sublimes  at 
250°C.,  hence  it  should  not  be  heated  too  long  and  too  hot. 

In  the  precipitation  large  amounts  of  ammonium  salts  do  no  harm 
but  an  excess  of  ammonia  tends  to  prevent  the  formation  of  the 
precipitate. 

If  cobalt  be  present  in  considerable  amount  the  solution  should  be 
diluted  to  100  c.c.  for  every  0.10  gram  of  cobalt. 

The  dimethylglyoxime  method  when  properly  modified  to  suit  the 
samples  makes  an  excellent  method  to  determine  the  nickel  in  ores. 

The  reagent  is  expensive.  It  may  be  recovered  by  mixing  the  nickel 
salt  to  a  paste  with  water,  warming  with  potassium  cyanide,  filtering 
hot  and  precipitating  the  oxime  with  acetic  acid. 

High  silicon  steels  should  have  the  silicon  removed  before  precipitat- 
ing the  nickel.  If  the  nickel  content  is  less  than  0.100  per  cent,  it  is 
best  to  carry  out  the  ether  separation  for  nickel  as  given  on  page  154. 

REFERENCES: 

BRUNK,  Z.  angew.  Chem.,  XX,  834. 
IBBOTSON,  Chem.  News,  CIV,  224. 

PARR  and  LINDGREN,   Trans.  Am.  Brass  Founders  Assoc.,  V,  120, 
describe  a  method  for  titrating  the  nickel  dimethylglyoxime. 

THE  DETERMINATION  OF  COBALT  IN  STEEL 

Cobalt  is  present  to  some  extent  in  all  samples  of  iron  and  steel  that 
contain  nickel.  It  is  now  being  intentionally  introduced  into  some  va- 
rieties of  high-speed  steel. 

Cobalt  is  separated  from  most  of  the  iron  in  a  hydrochloric  acid  solu- 


140  METALLURGICAL  ANALYSIS 

tion  by  means  of  the  ether  separation,  along  with  nickel,  manganese, 
copper,  vanadium,  aluminum  and  chromium.  In  this  solution  the  nickel 
and  cobalt  are  separated  from  the  other  elements  by  means  of  hydrogen 
sulfide.  If  cobalt  is  present  in  small  amounts  it  is  best  separated  from 
the  nickel  by  Ilinsky  and  Knorre's  reagent  (nitroso-/3-naphthol) .  If 
present  in  large  amounts  it  is  best  to  deposit  the  cobalt  and  nickel  to- 
gether electrolytically  and  then  dissolve  the  deposit  and  precipitate  the 
nickel  with  dimethylglyoxime. 

Process  of  Analysis. — Dissolve  1  to  5  grams  of  the  sample  in 
30  c.c.  of  HC1,  sp.  gr.  1.1.  When  dissolved  add  a  few  drops  of 
HF,  warm,  and  add  gradually  1  or  2  c.c.  of  HNO3  to  oxidize  the 
iron.  Then  carry  out  the  ether  separation  as  directed  under 
vanadium  on  page  154,  until  the  ether  has  all  been  boiled  off. 
Heat  to  boiling  and  precipitate  copper  with  H2S,  filter  and  wash. 
Add  sodium  carbonate  to  the  filtrate  until  the  solution  is  alkaline, 
then  acetic  acid  until  it  is  faintly  acid,  then  5  grams  of  sodium 
acetate,  dilute  to  100  c.c.,  heat  to  70°  and  pass  H2S  through  solu- 
tion for  one  hour.  Filter  through  a  filter  paper  on  which  has 
been  packed  macerated  filter  paper  and  wash  with  a  4  per  cent. 
HC1  solution  saturated  with  H2S  to  remove  all  manganese  sul- 
fide. The  filtrate  should  be  tested  for  cobalt.  Ignite  the  precipi- 
tate until  all  the  paper  has  been  burned  off. 

Dissolve  the  precipitate  in  strong  HC1  and  a  little  HNO3, 
add  5  c.c.  of  H2SC>4  and  evaporate  until  fumes  of  H2SO4  appear. 
The  procedure  from  this  point  depends  upon  whether  the  cobalt 
is  present  in  large  or  small  amounts. 

If  cobalt  is  present  in  amount  less  than  2  or  3  per  cent.,  dilute 
the  solution  to  100  c.c.,  add  10  c.c.  of  concentrated  HC1  and  a  suf- 
ficient amount  of  nitroso-0-naphthol  solution.  Allow  the  precipi- 
tate to  settle  for  several  hours,  filter,  wash  with  a  hot  10  per 
cent.  HC1  solution,  then  with  water  until  the  acid  is  removed. 
Ignite  the  precipitate  until  the  carbon  is  all  burned  off,  cool  the 
crucible,  dissolve  the  cobalt  oxide  in  HC1,  add  H2SO4,  evaporate 
to  dryness,  and  ignite  to  a  low  red  heat,  and  weigh  the  cobalt 
as  CoSO4  containing  38.04  per  cent,  cobalt. 

If  the  cobalt  is  present  in  large  amounts  precipitate  it  with 
the  nickel  as  follows:  Neutralize  the  sulfuric  acid  solution  of 
cobalt  and  nickel  obtained  above  with  NH4OH  and  add  30  c.c. 
of  NH4OH,  sp.  gr.  0.90,  in  excess,  dilute  to  100  c.c.  and  electrolize 


THE  DETERMINATION  OF  COBALT  IN  STEEL  141 

the  solution  using  a  gauze  cathode  and  a  current  of  2  amperes. 
Deposition  should  be  complete  in  one  hour.  To  test  the  com- 
pleteness of  the  deposition  withdraw  a  few  drops  of  the  solution 
by  means  of  a  pipette  and  add  it  to  a  drop  of  (NH4)2  S  on  a  white 
plate.  If  no  brown  color  appears  the  deposition  is  complete. 
Remove  the  cathode,  wash  with  pure  water,  rinse  with  alcohol, 
dry  at  105°  and  weigh  the  cobalt  plus  nickel.  Dissolve  the  pre- 
cipitated metals  in  strong  HC1,  dilute  to  100  c.c.,  and  precipitate 
any  nickel  that  may  be  present  as  directed  under  the  dimethyl- 
glyoxime  method.  Subtract  the  weight  of  the  nickel  from  the 
combined  weights  of  the  nickel  and  cobalt. 

Nitroso-/3-naphthol  Solution. — Dissolve  8  grams  of  the  solid 
in  300  c.c.  of  cold  glacial  acetic  acid  and  dilute  with  300  c.c.  of 
water.  The  solution  should  be  made  fresh  each  month. 

Notes  on  the  Process. — The  separation  of  cobalt  and  nickel  from  man- 
ganese and  iron  by  precipitation  from  a  weakly  acid  solution  must  be 
carried  out  carefully  as  some  of  the  cobalt  and  nickel  will  escape  pre- 
cipitation if  the  solution  is  too  acid  and  some  manganese  will  precipitate 
if  the  solution  is  too  nearly  neutral.  The  filtrate  should  be  tested  as 
follows:  evaporate  to  50  c.c.,  add  an  excess  of  (NH4)2S,  acidify  with  an 
excess  of  acetic  acid  and  warm  the  solution.  If  nickel  or  cobalt  be 
present  a  precipitate  will  remain. 

Nitroso-/3-naphthol  also  precipitates  copper,  chromium  and  iron  but 
does  not  precipitate  aluminium,  lead,  cadmium,  manganese,  nickel, 
mercury,  and  zinc. 

The  cobalt  nitroso-/3-naphthol  precipitate  is  very  voluminous,  hence 
it  is  not  advisable  to  precipitate  large  amounts  of  cobalt  in  this  way. 
Its  formula  is  [C10H60(NO)]3Co. 

The  cobalt  precipitate  may  be  ignited  in  a  Rose  crucible  with  oxalic 
acid  until  all  the  carbon  is  burned  off  and  finally  reduced  to  metal  by 
igniting  in  a  current  of  hydrogen.  It  is  difficult  to  eliminate  all  of  the 
carbon. 

The  nickel  may  be  determined  in  the  filtrate  from  the  cobalt  by  evapo- 
rating with  10  c.c.  of  H2S04  to  destroy  the  nitroso-/3-naphthol  and 
precipitating  with  dimethylglyoxime  or  KOH  and  bromine. 

The  electrolytic  deposit  of  cobalt  is  generally  brown  or  black  and  the  • 
results  tend  to  be  a  trifle  high.     If  too  small  an  amount  of  NH4OH  is 
used  some  nickel  or  cobalt  oxide  may  deposit  on  the  anode,  while  too 
large  an  amount  retards  the  deposition  of  the  metals.     Nitrates  should 
be  absent. 


142  METALLURGICAL  ANALYSIS 

Nickel  and  cobalt  also  precipitate  well  electrolytically  from  solutions 
of  cyanides,  oxalates,  and  in  the  presence  of  alkaline  acetates,  tartrates, 
citrates  and  phosphates. 

REFERENCES: 

FUNK,  Z.  anal.  Chem.,  45,  562  (1906).     Sulfide  precipitation. 
ILINSKY  and  KNORRE,  Ber.,  18,  699,  2728  (1885).    Nitroso-/3-naphthol. 
COPAUX,  Chem.  News,  87,  291  (1903).     Nitroso-/3-naphthol  method. 
SMITH,  "Electro-analysis,"  122. 
MELLOR,  "Quantitative  Inorganic  Analysis,"  389,  394. 


CHAPTER  X 

THE  DETERMINATION  OF  VANADIUM  IN  STEEL 

Very  small  amounts  of  vanadium  in  steel  seem  to  profoundly  alter 
some  of  the  properties  of  the  metal.  Hence  it  has  become  necessary 
to  be  able  to  determine  the  vanadium  very  accurately.  In  all  cases, 
however,  when  the  analysis  shows  the  presence  of  very  small  percent- 
ages of  vanadium  the  quantitative  results  should  be  confirmed  by  a 
qualitative  test.  The  test  is  given  on  page  156. 

THE  MANGANESE  DIOXIDE-PERMANGANATE  METHOD 

The  following  method  gives  very  good  results  and  no  element  present 
in  steel  interferes.  It  depends  upon  the  selective  oxidation  of  ferrous 
sulfate  in  the  presence  of  vanadyl  sulfate  by  manganese  dioxide.  The 
vanadyl  sulfate  is  titrated  by  adding  an  excess  of  standard  permanga- 
nate, the  excess  being  titrated  by  sodium  arsenite. 

The  reactions  are: 


Fe2(S04)3+MnSO4+2H2O. 


7H2S04. 

It  is  essential  that  the  manganese  dioxide  be  of  the  natural  or  crystal- 
line variety  (pyrolusite)  and  that  it  be  not  too  fine.  It  should  pass  through 
a  120-mesh  sieve,  and  yet  settle  in  a  beaker  of  water  in  15  seconds.  The 
fine  precipitated  variety  will  oxidize  V202(S04)2. 

Process  of  Analysis.  —  In  a  500  c.c.  flask  a  2-gram  sample  of 
the  steel  or  iron  is  dissolved  in  a  mixture  of  50  c.c.  of  water  and 
12  c.c.  concentrated  H2S04  with  application  of  heat.  Then  1  c.c. 
of  HNO3  (sp.  gr.  1.42)  is  added  cautiously  to  oxidize  the  iron 
and  the  solution  is  boiled  for  a  few  minutes  to  remove  the 
nitrous  fumes.  Then  the  solution  is  diluted  with  30  c.c.  of  water, 
5  c.c.  of  phosphoric  acid  and  a  strong  solution  of  KMn04  is 
added  to  completely  oxidize  all  carbon,  etc.,  and  the  solution  is 

143 


144  METALLURGICAL  ANALYSIS 

boiled.  If  the  permanganate  or  the  resulting  MnO2  should 
disappear,  not  enough  permanganate  has  been  used,  and  more 
should  be  added.  Now  ferrous  sulfate  is  added  to  reduce  the 
Mn02,  HMnO4,  H2CrO4,  H3V04,  etc.,  and  the  solution  is  again 
boiled  to  remove  any  possible  nitrous  fumes.  Then  distilled 
water  is  added  to  make  the  volume  about  250  c.c.,  N/10  KMn04 
added  until  the  solution  is  pink,  and  the  solution  cooled  to  tap 
water  temperature.  Ferrous  sulfate  solution  is  now  added  until 
all  reducible  compounds,  including  chromic  and  vanadic  acids, 
are  reduced.  Only  enough  ferrous  sulfate  should  be  added  to  be 
certain  that  there  is  a  decided  excess  present.  A  solution,  1  c.c. 
of  which  is  equal  to  about  0.01  gram  of  iron,  is  the  one  used. 
Now  about  1  gram  of  C.P.  Mn02  is  added  and  the  solution  shaken 
vigorously.  After  two  minutes  a  drop  is  tested  with  ferricyanide 
on  a  white  plate  to  see  if  the  iron  is  completely  oxidized.  It 
generally  takes  from  four  to  six  minutes.  At  the  end  of  each 
minute  the  solution  is  tested  for  ferrous  iron  until  none  is  pre- 
sent and  the  shaking  is  continued  for  about  one-half  minute 
longer.  It  should  be  noted  that  a  bluish  color  will  always  be 
obtained  in  the  presence  of  vanadyl  sulfate  after  the  test  drop 
has  stood  for  a  few  seconds.  The  end  should  be  taken  when  the 
test  does  not  show  blue  immediately.  The  blue  color  which 
forms  after  a  few  seconds,  even  when  there  is  no  ferrous  iron 
present,  is  due  to  .the  reduction  of  ferri-  to  ferrocyanide  by  the 
vanadyl  sulfate.  One  can  become  familiar  with  this  end  point 
by  adding  a  drop  of  ferric  sulfate  containing  vanadyl  sulfate  to 
a  drop  of  ferricyanide  on  a  white  plate. 

The  MnO2  oxidizes  the  ferrous  sulfate  to  ferric  sulfate,  but 
does  not  oxidize  the  vanadyl  sulfate  (V2O2(SO4)2).  Then  the 
MnO2  is  filtered  off  on  an  asbestos  mat,  using  suction.  From  a 
burette  a  standard  solution  of  KMnO4  is  added  until  a  pink 
tinge  is  present  in  the  solution,  then  1  c.c.  more  is  added  and  the 
solution  shaken  and  after  one  minute  the  excess  permanganate  is 
titrated  with  Na3As03  solution.  The  end  point  is  very  sharp. 
If  at  this  point  the  operator  is  not  satisfied  with  this  tit  ration, 
the  excess  arsenite  may  be  oxidized  with  KMn04,  ferrous  sul- 
fate again  added,  then  oxidized  with  MnO2  as  before,  and  the 
titration  repeated,  thus  giving  a  check  on  the  titration.  A 
blank  determination  must  be  run  on  a  vanadium-free  steel,  and 


THE  DETERMINATION  OF  VANADIUM  IN  STEEL      145 

the  result  deducted.  The  blank  generally  amounts  to  about 
0.00075  gram  V.  The  time  required  is  about  one-half  hour  and 
the  results  are  very  satisfactory.  In  fact  the  accuracy  is  nearly 
that  of  a  phosphorus  determination. 

The  vanadium  steel  standard  furnished  by  the  Bureau  of  Standards 
was  analyzed  by  the  above  method.  The  result  of  the  Bureau  chemists 
is  0.143  per  cent.  V  and  the  average  of  the  cooperating  chemists  is  0.15 
per  cent.  V.  The  writer  obtains  the  following  results,  the  average  being 
0.143  per  cent.: 

0.140  0.138 

0.147  0.147 

0.143  0.143 

To  further  test  the  method,  2-gram  samples  of  vanadium-free  steel 
with  the  addition  of  ferrovanadium  containing  0.00684  gram  of  vanadium 
were  analyzed.  The  results  were  0.00680  and  0.00690  gram  V.  An- 
other sample  with  0.0342  gram  V  was  analyzed,  and  0.03432  gram  V 
was  found. 

To  test  the  effect  of  chromium  on  the  method,  the  Bureau  of  Stand- 
ards' sample  above  mentioned  was  analyzed  with  the  addition  of  0.100 
gram  Cr.  The  results  were  0.143  per  cent,  and  0.143  per  cent.  V,  show- 
ing that  chromium  has  no  effect  on  the  vanadium  results.  Scores  of 
other  determinations  have  been  made,  proving  the  accuracy  of  the 
method. 

The  KMnO4  solution  used  equals  0.001  gram  iron  per  cubic 
centimeter  and  the  arsenite  solution  has  the  same  strength. 
This  makes  the  KMnO4  equal  0.000914  gram  vanadium  per  cubic 
centimeter.  The  arsenite  solution  is  made  by  dissolving  about 
1.78  gram  As203  in  Na2C03  solution  and  diluting  to  2000  c.c. 
as  directed  on  page  85. 

Notes  on  the  Process. — The  ferricyanide  solution  should  contain  about 
10  per  cent,  hydrochloric  acid.  The  phosphoric  acid  is  used  to  dis- 
charge the  color  of  the  iron  so  as  to  make  the  end  point  sharp.  It  is 
added  at  the  time  directed  in  order  that  any  impurities  in  the  acid  may  be 
oxidized.  If  the  amount  of  vanadium  in  the  sample  is  very  low,  a  larger 
sample  should  be  used  with  a  corresponding  increase  of  phosphoric  acid. 

The  Mn02  may  be  used  over  and  over.  As  the  finer  particles  become 
dissolved  the  dioxide  becomes  slower  in  action. 

Ferrous  sulfate  must  not  be  used  in  the  titration  as  it  gives  an  in- 
10 


146  METALLURGICAL  ANALYSIS 

distinct  end  point  due  to  slight  reduction  of  vanadium  along  with 
permanganate. 

REFERENCES: 

DEMOREST,  J.  Ind.  Eng.  Chem.,  IV,  April,  1912. 

DETERMINATION  OF  VANADIUM  IN  FERROVANADIUM 

Ferrovanadium  may  contain  as  much  as  50  per  cent,  of  vanadium. 
Since  it  is  very  subject  to  segregation  care  must  be  taken  to  get  a  prop- 
erly representative  sample.  It  is  best  to  make  several  determinations 
and  average  the  results. 

Weigh  0.50  gram  of  the  finely  crushed  sample  and  place  in  a 
750  c.c.  flask.  Dissolve  with  50  c.c.  of  water  and  15  c.c.  of 
sulfuric  acid  using  heat.  When  the  sample  is  dissolved  add  2  c.c. 
of  nitric  acid  and  boil  to  expel  nitrous  fumes.  Then  add  strong 
permanganate  solution  until  the  liquid  remains  pink  when 
boiled.  Add  a  little  water  to  cool  the  solution  somewhat,  then 
add  ferrous  sulfate  solution  until  all  MnC>2  is  dissolved  and  boil 
vigorously  to  expel  any  nitrous  acid  formed  by  the  action  of  the 
ferrous  sulfate  on  the  nitric  acid.  Now  add  permanganate 
enough  to  color  the  solution  pink  and  cool  to  tap  water  tempera- 
ture. Dilute  to  400  c.c.  and  run  in  ferrous  sulfate  until  all 
yellow  tints  are  gone  from  the  liquid  and  it  becomes  blue  due 
to  the  presence  of  vanadyl  sulfate.  Then  add  about  10  c.c. 
more  so  that  there  is  an  excess  of  ferrous  sulfate  present.  Now 
add  2  grams  of  MnO2  (preferably  some  which  has  been  used 
before  or  has  been  shaken  with  ferrous  sulfate  and  dilute  sul- 
furic acid  to  dissolve  the  fine  particles).  Shake  the  flask  vigor- 
ously and  test  the  solution  for  ferrous  ions  after  each  minute. 
As  soon  as  a  test  is  obtained  which  does  not  show  blue  immedi- 
ately, cease  shaking,  filter  off  the  MnO2  and  titrate  the  vanadium 
with  permanganate  solution  of  about  N/10  strength.  Add  the 
permanganate  until  a  pink  tinge  is  obtained  which  does  not  go 
after  shaking  the  solution  a  minute,  then  add  a  few  drops  more 
and  titrate  back  with  a  standard  arsenite  solution. 

If  it  is  desired  to  check  the  titration,  add  ferrous  sulfate 
solution  again,  then  add  MnC>2  and  repeat  the  oxidation  of  the 
ferrous  sulfate  and  the  titration. 

When  there  is  a  large  amount  of  vanadyl  sulfate  present  the 


THE  DETERMINATION  OF  VANADIUM  IN  STEEL       147 

test  for  ferrous  ions  with  ferricyanide  must  be  observed  immedi- 
ately as  the  vanadyl  sulfate  will  quickly  reduce  the  ferricyanide 
to  ferrocyanide  and  the  test  will  turn  blue. 

The  ferrovanadium  may  easily  be  crushed  by  folding  it  in 
several  thicknesses  of  paper  and  hammering  on  an  anvil.  The 
ferrovanadium  is  then  separated  from  paper  and  dirt  by  means 
of  a  magnet. 

The  above  method  gives  very  satisfactory  results  for  either 
vanadium  steels  or  ferro  vanadiums.  No  elements  interfere. 
The  chief  points  to  attend  to  are  to  make  sure  that  all  oxidiz- 
able  elements  are  oxidized  by  the  permanganate  in  hot  solution 
and  all  nitrous  fumes  are  removed  by  boiling,  and  that  the  MnC>2 
used  is  of  the  right  kind.  It  must  be  crystalline  and  free  from 
all  excessively  fine  particles.  The  MnC>2  should  be  washed  with 
running  water  until  it  settles  perfectly  clear  in  15  seconds 
when  stirred  up  in  a  large  beaker. 

DETERMINATION  OF  CHROMIUM  AND  VANADIUM 

Process  of  Analysis. — Dissolve  the  proper  amount  of  sample 
in  50  c.c.  of  water,  12.  c.c.  of  sulfuric  acid  and  15  c.c.  of  nitric  acid. 
When  the  sample  is  all  dissolved,  boil  to  remove  oxides  of  nitro- 
gen, then  add  50  c.c.  of  water  and  strong  permanganate  solution 
until  an  excess  is  present  and  a  precipitate  of  Mn(>2  remains  after 
20  or  more  minutes'  boiling.  The  addition  of  permanganate  is 
to  oxidize  all  carbon,  etc.,  and  the  long  boiling  is  to  decompose 
the  permanganate  excess.  If  the  permanganate  is  not  all  de- 
stroyed by  the  boiling,  the  result  for  chromium  will  be  too  high. 

After  the  permanganate  is  all  destroyed  cool  the  solution  some- 
what and  filter  through  an  asbestos  mat  and  wash  a  few  times. 
Dilute  the  filtrate  to  300  c.c.,  add  30  c.c.  of  1  :3  sulfuric  acid  and 
titrate. 

To  titrate,  run  in  the  standard  ferrous  sulfate  solution  (N/50) 
until  all  brown  tints  are  gone,  indicating  complete  reduction  of 
the  chromic  and  vanadic  acids  to  chromium  and  vanadyl  sulfates, 
then  add  several  cubic  centimeters  more.  To  make  sure  that 
enough  ferrous  sulfate  has  been  added  one  may  test  a  drop  of 
the  solution  with  ferricyanide  on  a  porcelain  plate.  Now  add 
the  standard  permanganate  solution  (N/50)  until  a  pink  color 


148  METALLURGICAL  ANALYSTS 

is  obtained  which  remains  after  a  minute  of  stirring  of  the  solu- 
tion. Then  add  a  cubic  centimeter  more  and  titrate  the  excess 
of  permanganate  with  the  arsenite  solution.  The  iron  value  of 
the  permanganate  used  subtracted  from  the  iron  value  of  the 
total  amount  of  ferrous  sulfate  and  arsenite  multiplied  by  0.310 
gives  the  amount  of  chromium  present. 

Now  add  sufficient  ferrous  sulfate  to  the  solution  to  reduce  the 
probable  amount  of  vanadium  present,  add  a  gram  or  two  of 
the  prepared  MnC>2  and  shake  the  flask  until  a  test  with  ferri- 
cyanide  on  a  white  plate  shows  that  all  the  ferrous  sulfate  is 
oxidized,  filter  and  titrate  the  vanadium  with  standard  perman- 
ganate as  directed  under  the  method  for  vanadium  alone. 

Notes  on  the  Process.  —  A  blank  must  be  run  on  the  chromium  (as 
well  as  on  the  vanadium)  by  treating  a  chromium  and  vanadium-free 
sample.  After  the  permanganate  has  been  used  in  the  hot  solution  to 
oxidize  all  carbon,  etc.,  the  excess  is  decomposed  by  boiling.  How- 
ever, there  is  always  a  minute  trace  of  the  Mn02  (or  higher  oxide) 
left  in  solution  which  cannot  be  filtered  out,  and  this  is  reduced  when 
the  ferrous  sulfate  is  added  to  titrate  the  chromium.  Hence,  the 
necessity  to  run  a  blank  on  the  chromium.  This  blank  is  very  constant 
if  the  boiling  is  always  carried  on  the  same  length  of  time. 

The  reactions  involved  in  the  titrations  are  as  follows  : 

On  addition  of  ferrous  sulfate, 

,  and 


When  the  permanganate  is  added  only  the  vanadyl  sulfate  is  oxidized 
thus, 

5V2O2(SO4)2+2KMnO4+22H20  =  10H3VO4+K2S04+2MnSO4 
+7H2SO4. 

So,  if  the  ferrous  sulfate  and  arsenite  solutions  are  equal  cubic  centimeter 
for  cubic  centimeter  to  the  permanganate,  the  number  of  cubic  centi- 
meters of  ferrous  sulfate  plus  arsenite  used  minus  the  number  of  cubic 
centimeters  of  permanganate  used  to  oxidize  back  the  vanadium  is  the 
number  of  cubic  centimeters  of  ferrous  sulfate  required  to  reduce  the 
chromium  from  the  hexavalent  to  the  trivalent  state.  Since  the 
chromium  is  reduced  three  valences  and  the  iron  is  oxidized  simultane- 
ously one  valence  it  requires  three  atoms  of  iron  to  reduce  one  atom  of 
chromium  and  therefore  the  iron  value  of  the  ferrous  sulfate  used  multi- 


THE  DETERMINATION  OF  VANADIUM  IN  STEEL      149 

52 
plied  by  3  x  55  "04  giyes  tne  amount  of   chromium  present.     Since  the 

vanadium  is  only  changed  by  one  valence  by  the  permanganate,  the  iron 

r  i     r\r* 

value  of  the  permanganate  used  multiplied  by  55  ^4  gives  the  amount  of 

the  vanadium  present.     These  fractions  figure  out  to  be  0.3103  and  0.915 
respectively.     If  the  solutions  used  are  fiftieth  normal  their  values  are 

52 
*3v ^TfvTooo  or  0.0003466  gram  per  cubic  centimeter  for  chromium 

and  cATTivv  or  0.001021  gram  of  vanadium  per  cubic  centimeter. 


JOHNSON'S  METHOD  FOR  CHROMIUM  AND  VANADIUM 

This  method  is  quick  and  fairly  accurate  though  results  tend  to  run  a 
trifle  low.  Vanadium  and  chromium  are  determined  together  practi- 
cally as  quickly  as  either  one. 

Vanadium  and  chromium  are  oxidized  by  permanganate  to  vanadic 
and  chromic  acids  respectively.  Then  standard  ferrous  sulfate  reduces 
them  to  vanadyl  sulfate  and  chromium  sulfate,  and  standard  permanga- 
nate added  to  the  cold  dilute  solution  oxidizes  the  vanadium  only  back 
to  vanadic  acid.  If  the  standard  solutions  are  equal  to  each  other  cubic 
centimeter  for  cubic  centimeter,  the  ferrous  sulfate  minus  the  perman- 
ganate equals  the  ferrous  sulfate  required  to  titrate  the  chromium. 
Then,  if  a  little  potassium  ferricyanide  is  put  in  the  solution  the  vana- 
dium may  be  titrated  by  ferrous  sulfate  and  when  the  vanadic  acid  is  all 
reduced  any  ferrous  sulfate  added  in  excess  will  give  a  blue  color  with  the 
ferricyanide. 

Process  of  Analysis. — Dissolve  2  grams  of  steel  in  50  c.c.  of 
water  and  10  c.c.  of  sulfuric  acid  in  a  500  c.c.  beaker.  When  the. 
action  is  over,  add  60  c.c.  of  1.2  sp.  gr.  nitric  acid  to  oxidize  the 
iron  and  boil  two  minutes.  Then  add  200  c.c.  of  water  and  add  a 
strong  permanganate  solution  a  little  at  a  time  until  a  slight 
precipitate  of -MnO2  is  obtained  that  does  not  dissolve  on  boiling 
20  minutes.  Now  cool  and  filter  through  a  Gooch  mat  and  wash 
several  times  with  dilute  sulfuric  acid. 

Return  the  filtrate  and  washings  to  the  beaker  and  add  30  c.c. 
of  1.3  sulfuric  acid.  The  volume  should  now  be  made  about 
350  c.c.  and  the  solution  is  ready  to  be  titrated. 

Add  a  ferrous  sulfate  solution  of  about  a  fiftieth  normal 
strength  until  the  fluid  in  the  beaker  loses  all  brown  tints  and 


150  METALLURGICAL  ANALYSIS 

assumes  a  practically  colorless  shade  in  plain  vanadium  steels  or 
a  green  color  in  chrome  steels.  Then  add  a  few  more  cubic  centi- 
meters to  make  sure  enough  has  been  added.  Now  add  one- 
fiftieth  normal  permanganate  solution  slowly  and  with  vigorous 
agitation  of  the  solution  until  a  very  faint  pink  is  obtained  that 
persists  after  30  seconds'  stirring.  Should  even  as  much  as  5 
or  6  per  cent,  of  chromium  be  present  a  practiced  operator  can 
easily  detect  the  pink  tints  through  the  chrome  green.  The 
amount  of  ferrous  sulfate  and  permanganate  used  should  be  re- 
corded if  the  amount  of  chromium  is  desired  to  be  known.  The 
iron  value  of  the  ferrous  sulfate  minus  the  iron  value  of  the  per- 
manganate multiplied  by  0.3103  gives  the  amount  of  chromium. 

The  solution  is  now  ready  for  the  vanadium  titration.  Add 
1  c.c.  of  a  0.1  per  cent,  solution  of  potassium  ferricyanide  (always 
use  the  same  amount)  and  drop  in  slowly,  and  with  stirring,  the 
standard  ferrous  sulfate  until  a  drop  produces  a  green  color  free 
from  yellow  tints.  If  much  chromium  is  present  the  ferrous 
sulfate  is  added  until  the  green  chromium  color  begins  to  darken. 
It  is  well  to  add  from  time  to  time  during  the  titration  a  drop  of 
the  indicator  and  see  if  a  green  coloration  is  produced  at  the 
point  where  the  drop  mixes  with  the  solution.  The  iron  value 
of  the  ferrous  sulfate  multiplied  by  0.914  gives  the  amount  of 
vanadium  present. 

A  blank  must  be  run  on  a  steel  free  from  vanadium  but  other- 
wise of  similar  composition.  Also,  it  is  best  to  run  at  the  same 
time  a  vanadium  determination  on  a  steel  containing  a  known 
amount  of  vanadium. 

Notes  on  the  Process. — The  presence  of  chromium  increases  the 
blank.  If  copper  is  present  it  will  precipitate  out  when  the  ferricyanide 
is  added.  In  such  a  case  the  ferricyanide  is  added  before  the  MnC>2  is 
filtered  off  and  the  copper  ferricyanide  filtered  off  with  the  Mn02. 
If  a  further  precipitate  is  produced  when  the  ferricyanide  is  added  for 
the  titration,  another  determination  is  run  using  double  the  amount  of 
ferricyanide  to  precipitate  the  copper.  Nickel,  if  present,  will  also 
slowly  precipitate  with  the  ferricyanide.  Molybdenum  does  not  inter- 
fere. If  the  sample  is  a  tungsten  steel,  when  it  is  dissolved  it  should  be 
digested  until  the  precipitated  tungstic  acid  is  a  bright  yellow.  Then 
enough  permanganate  should  be  added  to  cause  the  precipitate  of 
tungstic  acid  to  be  colored  chocolate  by  the  Mn02  formed. 


THE  DETERMINATION  OF  VANADIUM  IN  STEEL       151 

Ferrovanadium  is  analyzed  as  a  steel  except  that  a  smaller  sample  is 
used  (0.5  gram) .  To  titrate,  f erricyanide  indicator  is  added,  then  ferrous 
sulfate  until  the  light  blue  of  the  vanadyl  salt  is  darkened  slightly. 
The  amount  of  ferrous  sulfate  is  noted,  then  standard  permanganate  is 
added  until  a  rose  tint  is  obtained.  From  the  amounts  of  permanga- 
nate and  ferrous  sulfate  used,  the  vanadium  and  chromium  are  calculated. 
The  vanadium  present  is  obtained  by  multiplying  the  iron  value  of  the 
permanganate  used  by  0.914.  The  chromium  is  obtained  by  subtracting 
the  iron  value  of  the  permanganate  from  the  iron  value  of  the  ferrous 
sulfate  used  and  multiplying  by  0.3103.  The  permanganate  used  should 
be  about  N/10. 

It  is  absolutely  essential  in  vanadium  and  chromium  titrations  when 
coming  back  with  permanganate  to  add  the  permanganate  until  three 
drops  give  a  faint  pink  which  remains  visible  after  30  seconds'  stirring. 
The  ferrous  sulfate  should  be  added  until  three  drops  produce  a  distinct 
darkening  of  the  green  but  not  a  blue.  A  better  way  is  to  add  an  excess 
of  permanganate  and  titrate  the  excess  with  arsenite. 

Ferrovanadium  containing  much  silicon  may  dissolve  very  difficultly. 
After  as  much  has  dissolved  as  will  in  sulfuric  and  nitric  acid  a  cubic 
centimeter  of  hydrofluoric  acid  should  be  added  and  the  solution  evapo- 
rated to  fumes  to  expel  the  hydrofluoric  acid. 

REFERENCES: 

JOHNSON,  "Chemical  Analysis  of  Special  Steels,  Steel  Making  Alloys 

and  Graphites." 
CRITES,  J.  Ind.  Eng.  Chem.,  Ill,  574. 

METHOD  OF  CAIN  AND  HOSTETTER  FOR  VANADIUM 

It  has  long  been  known  that  when  ammonium  phosphomolybdate  is 
precipitated  from  a  solution  containing  vanadium  the  precipitate 
carries  down  with  it  vanadium  and  has  a  brick  red  color.  Cain  and 
Hostetter  have  shown  that  under  the  proper  conditions  the  vanadium  is 
completely  precipitated,  although  it  is  not  precipitated  at  all  with 
molybdic  acid  alone. 

Moreover,  Cain  and  Hostetter  have  shown  that  after  the  precipitate 
is  dissolved  in  concentrated  sulfuric  acid  the  vanadium  is  reduced  in  the 
concentrated  acid  solution  to  vanadyl  sulfate,  that  is,  to  tetravalent 
vanadium,  by  means  of  hydrogen  peroxide.  The  excess  of  peroxide  is 
driven  off  by  heating  the  solution  until  the  sulfuric  acid  fumes  strongly. 
Then  the  solution  is  diluted  and  the  vanadium  titrated  to  vanadic  acid 
(pentavalent  vanadium)  by  standard  permanganate  solution. 

The  method  is  especially  valuable  when  determining  vanadium  in 


152  METALLURGICAL  ANALYSIS 

materials  containing  a  very  small  percentage  of  vanadium,  as  samples  as 
large  as  even  50  grams  may  be  used.  Furthermore,  the  method  has  the 
very  great  advantage  of  affording  qualitative  confirmation  of  the  pres- 
ence of  vanadium. 

Process  of  Analysis. — For  steels  containing  vanadium,  chro- 
mium, nickel,  titanium,  manganese,  molybdenum,  singly  or  in 
combination,  dissolve  an  amount  of  drillings  estimated  to  contain 
2  to  10  mg.  of  vanadium  in  nitric  acid  (sp.  gr.  1.135),  boil  till 
free  from  fumes,  oxidize  with  permanganate  solution,  dissolve 
the  manganese  dioxide  with  potassium  nitrite  solution,  and  boil 
till  free  from  fumes.  In  other  words,  prepare  the  solution  ex- 
actly as  for  a  phosphorus  determination,  examining  any  insoluble 
residue  for  vanadium.  Nearly  neutralize  with  NH4OH  (0.96) 
and  add  an  amount  of  sodium  phosphate  solution  containing 
at  least  ten  times  as  much  phosphorus  as  there  is  vanadium  pres- 
ent. Bring  the  solution  to  boiling,  remove  from  the  plate  and 
add  at  once  the  usual  necessary  excess  of  the  molybdate  reagent 
to  precipitate  the  amount  of  phosphoric  acid  added.  Agitate 
for  a  minute  or  so,  when  it  will  be  found  that  the  precipitate 
settles  rapidly.  Filter  the  supernatant  liquid  by  suction  through 
an  asbestos  filter,  and  wash  three  times  by  decantation  with  hot 
acid  ammonium  sulfate  solution,  pouring  the  washing  liquid 
through  the  filter.  The  last  wash  solution  should  be  decanted  off 
as  completely  as  possible  from  the  precipitate  in  the  flask  and 
the  filter  should  be  sucked  dry.  Fit  the  rubber  stopper  carrying 
the  filter  funnel  to  a  small,  dry  bottle  and  pour  hot,  concentrated 
sulfuric  acid  on  the  filter  to  dissolve  the  small  amount  of  pre- 
cipitate thereon.  This  dissolves  quickly  and  the  solution  is 
drawn  through  by  suction  into  the  bottle.  Transfer  the  con- 
tents of  the  bottle  to  the  flask  in  which  precipitation  was  made, 
wash  the  bottle  once  with  concentrated  sulfuric  acid,  adding  the 
washings  to  the  flask.  For  every  10  mg.  of  phosphorus  present 
a  final  volume  of  5  to  8  c.c.  of  concentrated  sulfuric  acid  is  neces- 
sary. Heat  the  contents  of  the  flask  until  solution  takes  place, 
add  a  few  drops  of  nitric  acid  (1  :25),  and  when  fumes  are  com- 
ing off  strongly  remove  the  flask  from  the  plate,  cool  and  reduce 
the  vanadium  by  successive  small  additions  of  hydrogen  peroxide. 
Replace  on  the  hot  plate,  fume  for  four  or  five  minutes,  cover 
the  flask,  cool,  dilute  so  as  to  secure  an  acidity  of  one  part  to 


THE  DETERMINATION  OF  VANADIUM  IN  STEEL      153 

five  by  volume,  and  titrate  at  a  temperature  of  70°  to  80°C.  with 
0.01  N  permanganate.  The  condition  as  to  acidity  and  tem- 
perature must  be  closely  observed  in  order  to  secure  a  satisfactory 
end  point. 

For  steels  of  the  above  classes  containing  tungsten,  the  only 
change  necessary  is  to  dissolve  in  aqua  regia,  dilute  with  hot 
water,  filter  off  the  tungstic  acid,  nearly  neutralize  with  NH4OH, 
and  add  10  grams  solid  ammonium  nitrate  for  every  100  c.c.  of 
the  final  volume  before  precipitating  as  above  described.  If  de- 
sired, the  tungstic  acid  on  the  filter  may  be  dissolved  in  a  small 
amount  of  sodium  hydroxide  solution  (free  from  vanadium), 
acidified  with  nitric  acid  and  tested  for  vanadium  with  hydrogen 
peroxide. 

Notes  on  the  Process. — The  presence  of  vanadium  in  the  phospho- 
molybdate  precipitate  is  shown  by  the  yellow  to  orange  color  of  the  cold, 
concentrated  sulfuric  acid  solution  of  the  precipitate,  as  little  as  0.05 
mg.  of  vanadium  showing  a  color  in  a  volume  of  25  c.c. 

In  carrying  out  the  reduction  of  the  vanadium  by  peroxide  it  is  nec- 
essary to  use  a  flask  rather  than  an  open  beaker.  If  the  latter  is  used, 
the  molybdenum  is  reduced  where  the  solution  creeps  up  the  sides  of  the 
beaker.  The  hydrogen  peroxide  is  added  in  small  quantities  to  the  cold, 
concentrated  acid  solution  with  agitation  of  the  solution,  until  the  solu- 
tion takes  on  a  deep  brown  color  owing  to  action  on  the  molybdate. 
This  brown  disappears  on  heating  and  is  followed  by  the  clear  greenish- 
blue  of  vanadyl  sulfate. 

All  nitric  acid  must  be  removed  by  heating  the  solution  to  dense 
fumes  before  reducing  by  peroxide.  Nitrous  fumes  easily  oxidize 
tetravalent  vanadium  to  the  pentavalent  state. 

The  time  required  is  about  a  half  hour  on  ordinary  steels.  The 
alloy  steels,  such  as  tungsten  steel,  require  more  time  in  order  to  get 
them  completely  dissolved  and  oxidized.  The  method  can  be  used  for 
ores  as  well  as  metals. 

If  the  volume  of  the  solution  from  which  the  precipitate  is  made  is  very 
large  and  especially  if  there  is  hydrochloric  acid  present,  it  is  best  to  add 
10  grams  of  ammonium  nitrate  to  each  100  c.c.  Potassium  nitrate  or 
nitric  acid  solutions  should  not  be  used  to  wash  the  precipitate  as  it  is 
more  or  less  soluble  in  them.  Also  the  temperature  of  precipitation 
should  be  high  as  directed. 

REFERENCE : 

CAIN  and  HOSTETTER,  J.  Am.  Chem.  Soc.,  IV,  250. 


154  METALLURGICAL  ANALYSIS 

PEROXIDE  REDUCTION  METHOD  FOR  FERROVANADIUM 

The  writer  has  made  use  of  the  discovery  of  Cain  and  Hostetter  that 
hydrogen  peroxide  (or  alkali  peroxide)  reduces  vanadic  acid  in  strong 
sulfuric  acid  solution  to  determine  the  vanadium  in  ferrovanadium. 

The  process  is  as  follows :  Dissolve  ^  gram  of  the  sample  in 
30  c.c.  of  water  and  15  c.c.  of  sulfuric  acid.  When  action  ceases 
add  5  c.c.  of  nitric  acid  and  boil  until  all  nitrous  fumes  are  ex- 
pelled, then  add  potassium  permanganate  solution  until  an  excess 
is  present.  Evaporate  to  fumes  of  sulfuric  acid  and  fume  heavily 
for  several  minutes  to  expel  all  nitric  acid.  Cool  and  add  10 
c.c.  of  hydrogen  peroxide  ("Dioxygen"  is  good).  Evaporate  to 
fumes  of  sulfuric  acid,  cool  and  add  5  c.c.  more  of  hydrogen 
peroxide  and  evaporate  to  fumes  again  (the  liquid  has  a  great 
tendency  to  "  bump  ").  Continue  the  heating  until  heavy  billows 
of  fumes  have  been  filling  the  flask  for  about  four  minutes.  Cool 
the  solution  and  add  100  c.c.  of  water  and  heat  until  all  soluble 
salts  are  dissolved  and  the  solution  is  clear.  This  takes  con- 
siderable heating  and  stirring.  Now  dilute  to  300  c.c.  with  cold 
water  and  titrate  with  N/10  permanganate  until  the  solution 
takes  on  a  pink  tinge  which  does  not  disappear  on  stirring.  Then 
add  a  few  drops  more  and  shake  and  titrate  the  excess  of  per- 
manganate with  N/10  sodium  arsenite  solution.  The  number  of 
cubic  centimeters  of  permanganate  used  minus  the  number  of 
cubic  centimeters  of  arsenite  used  multiplied  by  0.005106  gives 
the  amount  of  vanadium  present. 

ETHER  SEPARATION  METHOD  FOR  VANADIUM 

The  following  method  for  vanadium  is  very  accurate  and  should  be 
used  in  important  cases. 

It  depends  upon  the  fact  that  when  a  solution  of  ferric  chloride  in 
HC1  is  shaken  up  with  sulphuric  ether  most  of  the  iron  will  go  into  the 
ethereal  solution  while  the  chlorides  of  vanadium,  nickel,  copper, 
manganese,  cobalt,  chromium  and  aluminum  remain  entirely  in  the 
aqueous  solution.  The  conditions  for  securing  a  good  separation  are 
as  follows:  first,  the  chlorides  must  be  dissolved  in  HC1  of  between 
sp.  gr.  1.1  and  1.13;  second,  the  volume  of  the  solution  must  be 
small,  not  exceeding  50  c.c.;  and  third,  the  ether  must  be  free  from 
alcohol  and  must  be  saturated  with  HC1  by  previously  shaking  it  up 


THE  DETERMINATION  OF  VANADIUM  IN  STEEL      155 

with  5  to  10  c.c.  of  the  concentrated  acid.  Finally,  sulphates  are  said 
to  interfere  with  the  ether  separation  and  if  present,  as  is  sometimes 
the  case  in  applying  the  process  to  ores,  must  be  removed.  In  this 
case  the  iron  can  be  precipitated  by  NH4OH  and  then  dissolved  in  HC1 
and  the  ether  separation  applied  to  this  solution.  Part  of  the  nickel 
will  be  in  the  filtrate  from  the  iron. 

Process. — Dissolve  5  grams  of  the  drillings  in  30  c.c.  of  dilute 
HC1  (1.1)  in  a  small  covered  beaker.  When  dissolved,  add  a  few 
drops  of  HF,  warm,  and  add  gradually  1  or  2  c.c.  of  HNO3  to 
oxidize  the  iron.  Evaporate  the  solution  to  about  10  c.c.  Cool 
it  and  pour  it  into  a  separatory  funnel  of  about  150  c.c.  capacity, 
having  a  very  short  stem.  Wash  out  the  beaker  with  warm  HC1 
of  1.13  sp.  gr.,  transferring  all  the  solution  to  the  funnel.  To 
keep  the  volume  small,  use  successive  small  portions  of  5  or  6  c.c. 
of  the  acid  in  washing.  The  total  volume  of  the  solution  in  the 
funnel  should  not  exceed  40  c.c.  Now  cool  the  funnel  and  its 
contents  and  cautiously  add  45  to  50  c.c.  of  ether  previously 
saturated  with  HC1.  Put  in  the  stopper  and  shake  the  funnel 
vigorously  for  five  minutes,  keeping  it  cool  by  holding  it  under 
running  water  from  the  tap.  Set  the  funnel  in  a  rack  and  let  it 
stand  until  the  ether  separates  and  the  line  between  the  two 
layers  of  liquid  is  sharp.  Then  take  out  the  stopper  carefully 
and  draw  off  the  aqueous  solution  down  to  the  stop-cock,  being 
careful  to  empty  the  tube.  Now  add  5  or  6  c.c.  of  HC1,  sp. 
gr.  1.13,  to  the  ether  in  the  funnel  and  shake  it  again.  Let  it 
separate  as  before  and  draw  off  the  acid,  adding  this  to  the  first 
extract.  It  is  desirable  to  use  as  little  acid  as  possible  in  the 
washing  as  it  takes  up  some  iron  from  the  ether  and  increases 
that  to  be  subsequently  removed  from  the  aqueous  solution. 

During  the  whole  operation  the  ether  and  the  funnel  should 
feel  cool  to  the  hand;  if  allowed  to  become  too  warm,  the  vapor 
pressure  may  blow  the  stopper  out  of  the  funnel.  The  aqueous 
solution  contains  some  dissolved  ether,  a  little  ferric  chloride 
(which  should  not  exceed  2  per  cent,  of  that  in  the  original  solu- 
tion) and  the  whole  of  the  chlorides  of  vanadium,  nickel,  cobalt, 
manganese,  aluminum  and  copper.  Set  the  flask  containing  this 
solution  on  a  water  bath  or  hot  plate  and  heat  it  until  the  ether 
is  expelled. 

Reduce  to  small  volume  in  a  casserole  and  remove  the  hydro- 


156  METALLURGICAL  ANALYSIS 

chloric  acid  completely  by  evaporation  to  dryness  with  concen- 
trated nitric  acid.  Take  up  in  strong  nitric  acid,  dilute  with 
water,  nearly  neutralize  with  sodium  hydroxide  solution  and 
pour  slowly  into  150-200  c.c.  of  10  per  cent,  sodium  hydroxide 
solution,  with  vigorous  stirring.  Filter,  retain  filtrate  and  repeat 
the  sodium  hydroxide  treatment  twice  with  the  insoluble  material, 
dissolving  it  each  time  in  dilute  nitric  acid.  In  these  latter  treat- 
ments the  volume  of  sodium  hydroxide  solution  may  be  smaller. 
The  filtrates  now  contain  the  vanadium.  They  are  combined 
and  made  nearly  neutral  or  faintly  alkaline  to  litmus  paper  by 
cautiously  adding  dilute  nitric  acid.  Precipitate  the  vanadium 
by  an  excess  of  fresh  mercurous  nitrate  solution.  The  mercurous 
vanadate  is  filtered  after  a  short  digestion  on  the  steam  bath, 
washed  with  1  per  cent,  mercurous  nitrate  solution  (the  filtrate 
being  tested  by  adding  more  mercurous  nitrate  solution  and 
digesting)  and  the  filter  paper  burned  off  in  a  platinum  crucible 
with  consequent  volatilization  of  the  mercury.  The  impure 
vanadium  pentoxide  remaining  is  fused  with  a  little  sodium  car- 
bonate, extracted  with  water,  the  extract  filtered,  in  order  to  get 
rid  of  the  small  amounts  of  iron  which  sometimes  contaminate 
the  vanadium  pentoxide  at  this  point,  and  the  precipitation  with 
mercurous  nitrate  repeated.  A  further  fusion  and  precipitation 
may  be  necessary.  The  vanadium  pentoxide  is  now  practically 
pure  and  is  fused  with  sodium  carbonate.  It  is  then  dissolved 
in  25  c.c.  of  1  :1  H2S04,  diluted  to  150  c.c.  and  a  stream  of  sul- 
fur dioxide  is  passed  through  the  boiling  hot  solution,  which  is 
then  boiled  until  the  SO  2  is  all  removed  and  titrated  hot  with 
permanganate. 

For  the  cadmium  carbonate  method  recommended  by  the  U.  S. 
Bureau  of  Standards  see  Reprint  161. 

QUALITATIVE  TESTS  FOR  VANADIUM  (AND  TITANIUM) 

The  color  of  the  phospho-molybdate  dissolved  in  strong  sulfuric  acid, 
according  to  Cain  and  Hostetter,  affords  a  good  qualitative  indication  of 
the  presence  or  absence  of  vanadium.  The  following  test,  elaborated 
by  Johnson,  also  is  good.  It  depends  upon  the  fact  that  in  dilute  acid 
solutions  hydrogen  peroxide  produces  a  brick  red  color  with  vanadium, 
due  to  the  formation  of  pervanadic  acid.  Titanium  under  the  same 
conditions  causes  a  yellow  color  when  the  peroxide  is  added.  If  both 


THE  DETERMINATION  OF  VANADIUM  IN  STEEL       157 

vanadium  and  titanium  are  present  a  mixed  color  is  obtained.  If  a 
clear  yellow  is  obtained  on  adding  the  peroxide  only  titanium  is  present, 
but  if  a  reddish  color  is  obtained  both  may  be  present.  If  ferrous  sul- 
fate  is  added  to  the  solution  after  the  hydrogen  peroxide  the  reddish 
color  of  the  vanadium  disappears  first,  leaving  the  yellow  of  the  titanium. 

Procedure. — Dissolve  0.5  gram  of  the  sample  in  10  c.c.  of  1:3 
sulfuric  acid,  heating  until  action  ceases.  Add  5  c.c.  of  con- 
centrated nitric  acid  and  boil  until  red  fumes  are  all  gone.  If 
tungsten  be  present,  filter.  Pour  half  of  the  solution  into  each 
one  of  two  6-in.  test-tubes.  Then  add  to  one  tube  5  c.c.  of  water 
and  to  the  other  5  c.c.  of  a  3  per  cent,  solution  of  hydrogen  per- 
oxide. If  vanadium  be  present  the  tube  to  which  the  peroxide 
was  added  will  be  distinctly  redder  than  the  other,  even  if  there 
be  only  a  few  hundredths  per  cent,  of  vanadium  in  the  sample. 
If  titanium  but  no  vanadium  be  present  the  color  will  be  a 
clear  yellow.  If  a  red  color  is  produced  vanadium,  and  possibly 
titanium,  is  present.  Add  N/20  ferrous  sulfate  1  c.c.  at  a  time, 
shaking  after  each  addition,  until  red  color  gradually  fades.  If 
titanium  be  present  the  red  will  change  to  a  clear  yellow.  If 
none  be  present  the  red  will  gradually  fade  out  without  chang- 
ing to  yellow. 


CHAPTER  XI 

THE  DETERMINATION  OF  TUNGSTEN,  CHROMIUM,  AND 
SILICON  IN  STEEL 

Tungsten  may  be  found  in  steel  in  amounts  up  to  25  per  cent,  and  is 
generally  accompanied  by  chromium  up  to  as  high  as  6  per  cent. 

When  a  steel  containing  tungsten  is  dissolved  in  a  mixture  of  nitric 
and  hydrochloric  acids  and  the  solution  is  evaporated  to  dryness  and  the 
residue  treated  with  hydrochloric  acid,  the  tungsten  is  left  insoluble  as 
W03  with  the  Si02.  In  order  to  render  the  W03  entirely  insoluble  more 
than  one  evaporation  to  dryness  is  necessary.  When  the  residue  is 
treated  with  sulfuric  and  hydrofluoric  acids  the  silica  is  driven  off  while 
the  tungstic  anhydride  is  left  behind.  The  tungstic  anhydride  is  always 
contaminated  with  ferric  oxide  and  must  be  purified  for  perfect  results. 

The  chromium  in  the  filtrate  is  oxidized  to  chromic  acid  and  titrated 
with  ferrous  sulfate. 

The  tungsten  is  usually  and  best  determined  gravimetrically  by 
weighing  as  W03,  but  since  the  W03  is  an  acid  anhydride  it  may  be 
determined  volumetrically  by  titrating  with  a  standard  alkali  solution. 

Tungsten  steels  are  very  hard  and  difficult  to  drill.  If  they  are 
annealed  at  750°C.  for  a  couple  of  hours  they  will  become  soft  enough 
to  drill.1 

Process  of  Analysis. — Place  2  grams  of  the  drillings  in  a  200 
c.c.  casserole  and  add  40  c.c.  of  hydrochloric  acid,  sp.  gr.  1.19, 
and  heat  nearly  to  boiling.  When  action  ceases,  add  from  time 
to  time  a  few  drops  of  nitric  acid  until  the  steel  is  entirely  decom- 
posed. In  this  way  the  sample  is  dissolved  without  the  separa- 
tion of  WO 3.  When  decomposition  is  complete  add  5  c.c.  HNO3, 
boil  the  solution  down  to  about  10  c.c.,  add  50  c.c.  of  water,  boil 
for  several  minutes  and  filter.  Wash  well  with  a  hot  5  per  cent. 
HC1  solution  until  all  ferric  chloride  is  removed.  Evaporate  the 
filtrate  to  hard  dryness,  add  15  c.c.  of  strong  HC1  and  heat  until 
all  iron  salts  are  dissolved,  dilute  to  50  c.c.,  heat  to  boiling  and 
filter,  wash  well  to  wash  out  all  iron.  Ignite  the  two  papers  and 

1  JOHNSON,  "Chemical  Analysis  of  Special  Steels,  Etc.,"  p.  197. 

158 


TUNGSTEN,  CHROMIUM,  AND  SILICON  IN  STEEL      159 

their  contents  in  a  platinum  crucible  until  all  paper  is  burned  off, 
but  do  not  heat  the  WO3  hotter  than  a  dull  red.  Cool  in  a 
desiccator  and  weigh. 

Add  three  drops  of  sulf  uric  acid  and  5  c.  c.  of  hydrofluoric  acid  and 
evaporate  off  the  acids  under  a  good  hood,  finally  driving  off  the 
sulf  uric  acid  by  heating  the  crucible  near  the  top.  Heat  to  a  dull 
red  and  weigh.  The  loss  in  weight  is  silica.  This  multiplied  by 
46.93  and  divided  by  the  weight  of  sample  equals  the  per  cent,  of 
silicon  in  the  sample. 

The  residue  of  tungstic  acid  always  contains  some  ferric  oxide 
and  possibly  some  chromic  oxide.  To  obtain  these,  fuse  the  resi- 
due with  5  grams  of  sodium  carbonate  until  all  tungstic  anhydride 
is  dissolved,  dissolve  the  cold  cake  with  hot  water  and  filter  off 
the  residue  of  ferric  oxide.  Wash  well  with  hot  water,  burn  off 
the  paper  and  weigh  the  residue.  Subtract  the  weight  so  ob- 
tained from  the  weight  of  the  impure  tungstic  oxide  after  the  silica 
was  driven  off  and  the  difference  is  the  weight  of  the  pure  WO3. 
Multiply  this  by  79.3  and  divide  by  the  weight  of  the  sample  to 
obtain  the  percentage  of  the  tungsten  in  the  sample. 

Meanwhile,  while  purifying  the  precipitate,  add  to  the  filtrate 
15  c.c.  of  sulf  uric  acid  and  15  c.c.  of  nitric  acid  and  evaporate 
until  copious  fumes  of  sulfuric  acid  appear  to  expel  all  the  hydro- 
chloric acid.  Add  25  c.c.  of  nitric  acid,  dilute  to  200  c.c.  and 
boil  until  all  salts  are  dissolved.  Then  add  a  strong  solution  of 
potassium  permanganate  a  little  at  a  time  until  a  pink  color  per- 
sists, and  then  boil  for  20  minutes  to  decompose  the  excess  per- 
manganate. A  precipitate  of  manganese  dioxide  should  remain. 
If  it  does  not,  not  enough  permanganate  has  been  added.  The 
solution  should  not  be  allowed  to  concentrate  much  or  manganese 
dioxide  will  go  into  solution  in  a  form  which  will  titrate  with 
ferrous  sulfate. 

Filter  off  the  manganese  dioxide  through  an  asbestos  mat,  wash 
a  few  times  with  water  and  cool  the  filtrate  to  tap-water  tempera- 
ture. Dilute  to  350  c.c.  and  titrate.  Run  in  a  N/10  ferrous  sul- 
fate solution  until  all  yellow  color  of  chromic  (and  vanadic)  acid 
has  gone  and  about  10  c.c.  excess.  Then  add  N/10  permanganate 
until  a  faint  pink  appears  in  the  chrome  green  solution  if  much 
chromium  is  present.  The  pink  should  persist  after  a  minute's 
shaking.  If  it  does  not,  add  more  until  it  does.  The  ferrous  sul- 


160  METALLURGICAL  ANALYSIS 

fate  used  minus  the  permanganate  used  multiplied  by  0.001733 
(if  the  solutions  are  N/10)  equals  the  chromium  present.  Or  the 
iron  value  of  the  ferrous  sulfate  minus  the  iron  value  of  the  per- 
manganate multiplied  by  0.31  gives  the  chromium  present. 

After  the  chromium  is  titrated  the  vanadium  may  be  titrated 
according  to  the  method  given  on  page  148. 

Notes  on  the  Tungsten  and  Chromium  Determinations. — When  the 
steel  is  dissolved  in  strong  hydrochloric  acid  as  above  directed  the  tung- 
stic  acid  does  not  separate  until  the  sample  is  dissolved  and  the  precipi- 
tate is  not  much  contaminated  with  iron.  Since  a  trace  of  tungstic  acid 
remains  in  solution,  also  some  silica,  it  is  necessary  to  evaporate  the 
nitrate  to  dryness  to  render  both  insoluble  by  dehydrating  the  tungstic 
acid  and  silicic  acid  forming  the  insoluble  anhydrides  W03  and  SiC>2. 
But  a  fairly  accurate  determination  of  tungsten  may  be  made  by  omit- 
ting the  evaporation  to  dryness. 

Tungstic  anhydride  is  volatile  if  ignited  at  a  much  higher  temperature 
than  a  dull  red,  hence  the  necessity  for  heating  carefully. 

There  will  always  be  a  little  W03  which  adheres  to  the  casserole  and 
cannot  be  removed  by  a  policeman.  It  can  be  removed  as  follows: 
When  the  casserole  is  well  washed  out  and  the  filter  paper  and  precipitate 
thoroughly  washed,  wet  a  piece  of  filter  paper  with  NH4OH  and  wipe 
out  the  casserole  with  it.  This  will  remove  all  the  tungstic  acid  adhering 
to  the  casserole.  Add  the  paper  to  the  other  two  papers  and  ignite 
them  all  together. 

If  the  chromium  in  the  filtrate  is  not  desired  and  a  tungsten  determina- 
tion alone  is  wanted,  it  is  not  necessary  to  evaporate  the  filtrate  from 
the  W03  to  dryness.  Proceed  as  follows:  Add  to  the  filtrate  20  c.c.  of 
1  : 1  hydrochloric  acid  solution  containing  0.5  gram  of  cinchonine.  The 
cinchonine  precipitates  the  tungsten  completely.  Heat  the  solution 
and  filter  and  wash  with  a  dilute  acid  solution  of  cinchonine.  Ignite 
the  precipitate  with  the  rest  of  the  precipitate  of  WO 3. 

When  the  filtrate  from  the  W03  is  evaporated  to  fumes  of  sulfuric  acid 
the  HC1  is  expelled.  This  is  necessary  before  the  chromium  is  deter- 
mined. The  sulfates  will  dissolve  slowly,  but  it  is  not  necessary  to  wait 
until  they  are  all  dissolved  before  adding  the  permanganate  to  oxidize 
the  chromium  to  chromic  acid.  The  reactions  involved  in  the  chromium 
determination  are  given  under  the  determination  of  vanadium  and 
chromium. 

If  the  presence  of  molybdenum  is  suspected,  the  filtrate  from  the 
fusion  of  the  W03  should  be  tested  for  molybdenum  as  directed  on 
page  164.  If  molybdenum  is  found  it  should  be  determined. 


TUNGSTEN,  CHROMIUM,  AND  SILICON  IN  STEEL      161 

Volumetric  Method  for  Tungsten. — Wash  the  precipitate  of 
WO3  obtained  as  above  directed  with  a  hot  dilute  hydrochloric 
acid  solution  until  the  iron  salts  are  gone,  then  wash  with  a  5 
per  cent,  solution  of  KNO3  until  the  washings  are  free  from  acid. 
It  is  not  necessary  that  the  W03  be  all  removed  from  the  casserole 
as  directed  for  the  gravimetric  method.  Put  the  filter  and  con- 
tents in  the  casserole,  run  in  from  a  burette  about  60  c.c.  of  a 
N/10  sodium  hydroxide  solution  and  stir  the  paper  about  until 
all  the  WO3  is  dissolved.  Then  add  a  few  drops  of  phenolphtha- 
lein  and  titrate  the  excess  of  soda  with  N/10  HC1  until  the  pink 
color  disappears.  The  number  of  cubic  centimeters  of  soda  used 
minus  the  number  of  cubic  centimeters  of  acid  used  multiplied  by 
0.0092  divided  by  the  weight  of  sample  used  and  multiplied  by 
100  gives  the  percentage  of  tungsten. 

The  titration  reaction  is  W03+2NaOH  =  Na2W04+H20.  If  the 
WO  3  is  very  impure  with  iron  the  end  point  of  the  titration  is  unsatis- 
factory. (See  J.  Am.  Chem.  Soc.,  IV,  477,  LINDE  and  TRUEBLOOD.) 

REFERENCES  FOR  THE  GRAVIMETRIC  METHOD: 

ARNOLD  and  IBBOTSON,  "Steel  Works  Analysis,"  161. 
MCFARLANE,  "Lab.  Notes  on  Iron  and  Steel  Analysis,"  211. 
JOHNSON,  "Chem.  Analysis  of  Special  Steels,  Steel-making  Alloys, 

Etc.,"  59. 

BLAIR,  "The  Chem.  Analysis  of  Iron,"  217. 
MCKENNA,  Proc.  Eng.  Soc.  Western  Pa.,  XVI,  119. 
WALTER,  Chem.  Ztg.,  XXXIV,  2. 
ZINBERG,  Stahl  u.  Eisen,  XXVIII,  1819. 
BARTONEC,  Chem.  Zenir.,  1909,  2017  (gravimetric  and  volumetric). 

Colorimetric  Determination  of  Chromium  when  Present  in  Small 
Amounts. — This  method  devised  by  Garrett  is  particularly  advanta- 
geous for  use  on  steels  containing  less  than  0.2  per  cent,  chromium.  It 
depends  upon  the  fact  that  disodium  1,8-dihydroxy-naphthalene  3,6- 
disulfonate  is  extremely  sensitive  to  chromate  solutions,  giving  a  pink 
color.  The  method  is  short  and  accurate. 

Process  of  Analysis. — Dissolve  from  0.2  to  0.4  gram  of  steel 
(depending  upon  the  amount  of  chromium  present)  in  10  c.c.  of 
1:3  sulfuric  acid  in  a  400  c.c.  flask.  When  solution  is  complete, 
add  %  c.c.  of  concentrated  nitric  acid  and  boil  nearly  to  dry  ness 
to  expel  nitrous  fumes  and  nitric  acid.  Do  not  use  more  nitric 
acid  than  directed.  Add  50  c.c.  of  10  per  cent,  sodium  hydroxide 
solution  and  1  gram  of  sodium  peroxide  and  boil  for  five  minutes. 
11 


162  METALLURGICAL  ANALYSIS 

There  must  be  no  peroxide  left  undecomposed,  as  it  would  reduce 
the  chromate  after  acidification.  Five  minutes'  boiling  is  suffi- 
cient. Cool  the  solution  to  room  temperature  and  dilute  to  200 
c.c.  in  a  calibrated  flask.  Filter  off  100  c.c.  and  add  to  the  filtrate 
2  c.c.  of  85  per  cent,  phosphoric  acid  and  8  c.c.  of  concentrated 
sulfuric.  This  heats  the  solution.  Immediately  add.  2  c.c.  of  1 
per  cent,  aqueous  solution  of  disodium  1,8-dihydroxy naphthalene 
3,6-disulfonate.  A  pink  to  cherry-red  color  develops,  depending 
upon  the  amount  of  chromium.  Allow  the  solution  to  stand  for 
15  minutes  and  then  compare  the  colors  obtained  from  the 
sample  and  a  standard  steel  by  any  convenient  colorimeter. 

Notes  on  the  Process. — The  standard  is  best  made  by  using  a  chro- 
mium-free steel  to  the  solution  of  which  is  added  a  desired  amount  of 
standard  bichromate  solution. 

There  is  a  slight  retention  of  chromium  by  the  iron  precipitate,  but 
since  the  standard  is  treated  in  the  same  way,  this  makes  little  error. 

Vanadium  interferes  with  the  method  by  giving  a  brownish  tint. 

Titanium  also  gives  a  red  color  with  the  reagent,  but  titanium  is  pre- 
cipitated out  with  the  iron.  The  error  due  to  the  vanadium  can  be 
avoided  by  adding  the  same  amount  of  vanadium  to  the  standard. 

REFERENCE  : 

GARRATT,  J.  Ind.  Eng.  Chem.,  V,  298. 


CHAPTER  XII 

DETERMINATION  OF  MOLYBDENUM  IN  STEEL 

When  an  acid  solution  of  a  molybdenum  steel  is  nearly  neutralized 
and  added  to  a  hot  sodium  hydroxide  solution  the  molybdenum  stays  in 
solution  as  sodium  molybdate  while  the  other  metallic  constituents  are 
precipitated  (except  perhaps  a  little  chromium).  The  sodium  molyb- 
date solution  is  filtered  off  and  the  molybdenum  is  precipitated  as  lead 
molybdate. 

Process  of  Analysis. — Place  2  grams  of  the  drillings  in  a  450  c.c. 
beaker  and  cover  them  with  50  c.c.  of  strong  hydrochloric  acid. 
Heat  to  the  boiling-point  and  add,  a  few  drops  at  a  time,  strong 
nitric  acid.  Continue  to  heat  the  solution  and  add  nitric  acid,  a 
few  drops  at  a  time,  until  the  sample  is  in  solution  and  the  iron 
is  oxidized.  Very  little  more  nitric  acid  should  have  been  added 
than  was  necessary  to  oxidize  the  iron.  A  black  film  of  carbona- 
ceous matter  will  remain.  Now  evaporate  to  beginning  pasti- 
ness, add  50  c.c.  of  hot  water  and  10  c.c.  of  hydrochloric  acid  and 
boil  a  few  minutes.  The  tungstic  acid  separates  if  there  be  any 
present.  Filter  and  wash  the  precipitate  with  hot  water  acidu- 
lated with  hydrochloric  acid.  To  the  filtrate  add  a  solution  of 
sodium  hydroxide,  shaking  the  flask  well  during  the  addition, 
until  most  of  the  free  acid  is  neutralized,  but  not  until  a  darkening 
in  color  takes  place.  Now  transfer  the  solution  to  a  separatory 
funnel. 

Open  the  stop-cock  of  the  funnel  so  that  the  solution  runs  out  in 
drops  and  allow  the  drops  to  fall  into  a  500  c.c.  graduated  flask 
containing  150  c.c.  of  a  6  per  cent,  solution  of  sodium  hydroxide 
heated  nearly  to  boiling.  Shake  the  flask  vigorously  while  the 
stream  of  drops  is  running  in.  This  is  important,  as  otherwise 
some  molybdenum  will  be  carried  down  with  the  ferric  hydroxide. 
Finally  wash  the  funnel.  The  iron  and  all  but  a  little  of  the 
chromium  are  precipitated  as  hydroxides.  A  small  amount  of 
the  chromium  goes  into  the  filtrate  as  chromate. 

163 


164  METALLURGICAL  ANALYSIS 

Fill  the  500  c.c.  flask  up  to  the  mark,  mix  well  by  inverting  and 
shaking  and  filter  through  a  large  paper  into  a  250  c.c.  graduated 
flask,  rejecting  the  first  few  cubic  centimeters  of  filtrate.  Trans- 
fer the  250  c.c.  of  filtrate  to  a  500  c.c.  beaker  and  add  hydrochloric 
acid  until  the  solution  just  becomes  acid,  using  methyl  orange  as 
indicator,  then  add  4  c.c.  of  hydrochloric  acid,  sp.  gr.  1.19,  in 
excess.  Add  a  few  drops  of  sulfurous  acid  to  reduce  the  small 
amount  of  chromic  acid  usually  present,  and  boil.  Add  40  c.c. 
of  ammonium  acetate  made  by  adding  30  per  cent,  acetic  acid  to 
strong  NH4OH  until  the  NH4OH  is  neutralized.  Now  add  40  c.c. 
of  a  1  per  cent,  lead  acetate  solution,  stir  well  and  filter  through  a 
close  filter  paper  and  wash  well  with  hot  water.  Ignite  in  a 
porcelain  crucible  and  weigh.  The  lead  molybdate  contains 
26.16  per  cent,  of  molybdenum. 

Notes  on  the  Process. — When  the  sample  is  dissolved  and  oxidized 
with  nitric  acid  a  little  molybdic  acid  may  precipitate,  and  would  appear 
with  the  tungstic  acid  if  any  were  present.  . 

The  treatment  with  soda  forms  sodium  molybdate  which  is  soluble, 
while  the  iron  separates  as  ferric  hydroxide.  If  the  acid  solution  is  not 
added  slowly  and  with  vigorous  stirring  the  ferric  hydroxide  will  carry 
down  with  it  some  molybdic  acid.  The  ammonium  acetate  is  added  to 
reduce  the  acidity  according  to  the  law  that  when  a  mixture  of  ions  are 
present  they  will  be  so  grouped  that  the  least  dissociated  compound  pos- 
sible will  be  formed,  in  this  case  acetic  acid  instead  of  hydrochloric  acid. 

If  much  tungsten  is  present,  the  W03  should  be  dissolved  in  sodium 
hydroxide,  diluted  to  50  c.c.,  hydrochloric  acid  added  until  the  solution 
is  acid  and  20  c.c.  excess  added  and  the  solution  evaporated  down  to  10 
c.c.,  diluted  to  50  c.c.  and  boiled,  the  W0a  filtered  off  and  the  filtrate 
added  to  the  main  filtrate. 

REFERENCES: 

'Chemical  News,  LXXXI,  269. 

ARNOLD  and  IBBOTSON,  " Steel  Works  Analysis." 

MCFARLANE,  "Lab.  Notes  on  Iron  and  Steel  Analysis." 

BLAIR,  "The  Chem.  Anal,  of  Iron." 

JOHNSON,  "Chem.  Anal,  of  Special  Steels,  Etc." 

Qualitative  Test  for  Molybdenum. — Dissolve  ^2  gram  of  the 
drillings  in  25  c.c.  of  1 : 1  HCL  Add  2  grams  of  KC1O3  and  heat 
until  the  residue  is  bright  yellow  if  tungsten  is  present.  Filter 
and  add  to  the  filtrate  10  grams  of  KOH  dissolved  in  10  c.c.  of 
water.  Boil  for  several  minutes.  Filter  and  pour  the  solution 


DETERMINATION  OF  MOLYBDENUM  IN  STEEL         165 

into  a  large  test-tube.  Add  HC1  until  crystals  of  KC1  begin  to 
form,  then  add  a  few  grains  of  granulated  tin  and  heat  just 
to  boiling  but  no  more.  Cool  and  add  J^  gram  of  KCNS.  If 
molybdenum  be  present  a  red  color  develops,  the  depth  of  the 
color  depending  upon  the  amount  of  molybdenum  present. 

The  precipitation  with  KOH  is  to  separate  out  the  iron  which 
would  also  give  a  red  color  with  KCNS.  The  solution  must  not 
be  heated  too  long  with  the  tin  present  or  the  delicacy  of  the 
test  will  be  impaired.  The  test  will  indicate  the  presence  of  as 
little  as  0.2  per  cent,  or  less. 


CHAPTER  XIII 
THE  DETERMINATION  OF  TITANIUM 

Titanium  may  be  present  in  steels  up  to  a  few  tenths  per  cent.  It  is 
generally  present  in  pig-iron  in  small  amounts.  In  ferrotitanium  there 
may  be  as  high  as  75  per  cent,  present.  Ores  contain  from  nearly  zero 
up  to  a  good  many  per  cent,  of  titanium. 

Titanium  may  be  determined  gravimetrically  by  weighing  as  Ti02  or 
volumetrically  by  reduction  with  zinc  to  trivalent  condition  followed  by 
titration  with  permanganate.  When  present  in  amounts  below  0.5 
per  cent,  it  is  best  determined  colorimetrically.  This  is  done  by  adding 
hydrogen  peroxide  to  the  5  per  cent,  sulfuric  acid  solution  and  pro- 
ducing a  yellow  color  which  is  compared  with  a  standard  solution  treated 
in  the  same  way.  The  peroxide  oxidizes  the  titanium  to  the  hexavalent 
form. 

Titanium  may  be  separated  from  iron  when  the  iron  is  divalent  by 
boiling  the  dilute  slightly  acid  solution,  when  the  titanium  precipitates 
out  as  titanic  acid.  Or  the  titanium  may  be  separated  from  the  iron 
when  to  the  acid  solution  containing  the  iron  in  the  ferrous  condition  is 
added  an  excess  of  ammonia  containing  enough  alkali  cyanide  to  form 
ferrocyanide  with  the  iron.  The  ferrocyanide  stays  in  solution,  while 
the  titanium  precipitates  as  Ti(OH)4.  This  precipitate  whether  made 
from  acid  or  alkaline  solution,  if  formed  from  a  solution  containing  large 
amount  of  iron,  is  always  impure.  If  the  precipitate  is  then  fused  with 
sodium  carbonate  and  the  fusion  is  extracted  with  water,  the  titanium 
remains  insoluble  as  sodium  titanate  while  phosphorus,  silica,  chromium, 
aluminum  and  vanadium  go  into  solution.  The  titanate  is  dissolved 
in  acid,  the  Ti(OH)4  is  again  precipitated  and  weighed  as  Ti02. 

Process  of  Analysis  (Colorimetric). — Add  to  1  gram  of  the 
sample  in  a  500  c.c.  flask  40  c.c.  of  1:3  sulfuric  acid.  Heat  to 
boiling  until  no  more  action  takes  place.  Pay  no  attention  to  any 
residue.  Dilute  to  250  c.c.  and  add  NH4OH  until  a  slight  pre- 
cipitate forms,  then  add  a  few  grams  of  sodium  thiosulfate  and  a 
few  drops  of  sulfuric  acid  or  enough  to  make  the  solution  clear. 
Heat  until  all  the  iron  is  reduced  as  shown  by  a  test  of  a  drop  with 
KCNS,  then  add  a  solution  containing  25  c.c.  of  water,  15  c.c, 

166 


THE  DETERMINATION  OF  TITANIUM  167 

of  NH4OH,  sp.  gr.  0.9,  and  10  grams  of  KCN.  Heat  to  boiling 
for  several  minutes.  Prepare  a  filter  by  shaking  two  9-cm.  filter 
papers  in  a  flask  until  well  macerated  and  then  pouring  the 
pulp  through  a  funnel  containing  a  platinum  cone.  Place  this 
funnel  in  a  suction  flask  and  pour  the  solution  through,  using 
suction.  The  solution  should  filter  quickly  to  prevent  oxida- 
tion of  the  iron.  Wash  well  with  water. 

Burn  the  paper  and  its  contents  in  a  platinum  crucible  until 
all  the  paper  is  consumed,  then  add  4  grams  of  KHS04  which  has 
been  previously  fused  to  remove  the  water  and  fuse  and  maintain 
at  a  bright  red  heat  for  several  minutes.  Cool,  then  add  water 
enough  to  half  fill  the  crucible  and  5  c.c.  of  sulfuric  acid,  and  heat 
until  the  cake  is  all  dissolved.  Cool,  transfer  to  a  Nessler  tube  or 
other  color  comparitor,  dilute  to  100  c.c.  and  add  3  c.c.  of  hydro- 
gen peroxide  (ordinary  3  per  cent,  solution).  If  titanium  is  pres- 
ent a  yellow  color  will  immediately  appear.  To  the  other  tube 
add  100  c.c.  of  5  per  cent,  sulfuric  acid,  3  c.c.  of  peroxide  and 
standard  titanium  sulfate  solution  a  little  at  a  time,  shaking  after 
each  addition,  until  the  color  matches  the  color  in  the  solution  of 
titanium  from  the  sample.  The  titanium  in  the  sample  will  then 
be  the  same  as  that  added  for  comparison. 

The  above  method  is  very  accurate,  only  requires  about  1% 
hours,  and  vanadium  does  not  interfere,  as  it  would  if  the  sam- 
ple were  compared  directly.  A  Government  standard  sample 
containing  0.073  per  cent.  Ti  gave  0.075  per  cent,  by  the  above 
method  even  when  3  per  cent,  of  vanadium  was  added. 

Gravimetric  Method. — Fuse  the  precipitate  obtained  above 
with  twenty  times  its  weight  of  sodium  carbonate  and  a  little 
KNO3  until  in  quiet  fusion  dissolve  in  hot  water  and  wash  with 
sodium  carbonate  solution  (5  per  cent).  Wash  at  least  ten 
times.  Place  the  paper  and  residue  of  sodium  titanate  in  a 
platinum  crucible  and  fuse  with  KHS04  at  a  bright  red  until  in 
clear  fusion.  Cool,  dissolve  in  hot  water  containing  sulfuric 
acid,  add  NH4OH  until  nearly  but  not  quite  alkaline,  then  a 
gram  or  so  of  thiosulfate  to  reduce  what  little  iron  may  be  present 
and  finally  add  a  solution  of  25  c.c.  of  water,  15  c.c.  of  NH4OH 
and  1  gram  of  KCN.  Heat  to  boiling  and  filter  through  a  pulp 
filter  as  above  directed.  Wash  well  to  remove  alkali  salts  and  if 
the  amount  of  titanium  is  not  high,  ignite  and  weigh  the  Ti(>2.  It 


168  METALLURGICAL  ANALYSIS 

should  be  ignited  over  the  blast.  If  the  sample  is  very  high  in 
titanium,  as  in  a  ferrotitanium,  the  precipitate  will  carry  down 
some  alkali  salts  and  should  be  dissolved  in  sulfuric  acid  1:3 
and  precipitated  again  with  NH4OH.  The  weight  of  the  pre- 
cipitate multiplied  by  0.6005  gives  the  titanium. 

Ores  are  analyzed  as  follows:  Place  1  gram  of  the  finely  ground 
sample  in  a  platinum  crucible,  add  10  grams  of  sodium  carbonate 
and  fuse  until  the  fusion  is  quiet.  Cool,  dissolve  in  hot  water 
and  wash  well  to  remove  as  much  silica  and  alumina  as  is  pos- 
sible. Ignite  the  paper  and  residue  in  a  platinum  crucible,  fuse 
with  KHSO4,  dissolve  in  hot  water  containing  5  c.c.  of  sulfuric 
acid  and  proceed  as  with  the  first  solution  of  the  metal  in  sulfuric 
acid  as  given  above,  for  either  the  colorimetric  or  gravimetric 
method. 

Notes  on  the  Process. — When  a  metal  is  dissolved  in  sulfuric  acid  it 
will  go  into  solution  mostly  as  ferrous  iron,  so  that  not  much  "thio- 
sulfate"  will  be  required.  When  the  sample  is  an  ore  more  care  will  be 
required  to  get  all  the  iron  reduced. 

The  precipitate  of  Ti(OH)4  from  an  alkaline  solution  has  no  tendency 
to  run  through  the  filter.  If  the  filter  is  a  pulp  one  the  filtration  will  be 
rapid  but  if  a  filter  paper  is  used  it  will  be  slow. 

Ti(OH)4  has  a  strong  tendency  to  stick  to  the  glass,  so  that  the  pre- 
cipitations should  all  be  made  in  the  same  flask.  Finally  it  is  well  to 
heat  the  flask  with  5  c.c.  of  strong  sulfuric  acid  until  it  fumes  strongly  and 
then  determine  the  titanium  thus  obtained  colorimetrically. 

There  must  be  no  fluorine  in  the  solution  to  be  analyzed  colorimetric- 
ally as  it  discharges  the  color  of  titanium  with  hydrogen  peroxide.  Also 
large  amounts  of  alkali  sulfates  effect  a  slight  weakening  of  the  color. 

Both  chromium  and  aluminum  precipitate  from  alkaline  solution  with 
titanium  and  should  be  removed  upon  solution  of  the  sodium  carbonate 
fusion  when  the  gravimetric  method  is  used.  They  do  no  harm  in  the 
colorimetric  method.  The  KN03  is  used  to  oxidize  the  chromium  to 
chromate. 

It  must  not  be  forgotten  that  KCN  is  very  poisonous  and  the  solution 
containing  it  must  not  be  made  acid  except  with  the  greatest  care  and 
in  a  good  hood. 

The  precipitate  of  Ti(OH)4  may  contain  a  little  nitride  after  ignition 
and  be  brown.  If  it  is,  it  should  be  fused  with  sodium  carbonate  again 
and  reprecipitated  from  a  solution  only  slightly  alkaline  with  NH4OH. 

REFERENCE : 

BORNEMAN  and  SCHIREMEISTER,  Metallurgie,  7,  71,  723. 


THE  DETERMINATION  OF  TITANIUM  169 

Standard  TiO2  Solution. — Ignite  pure  TiO2  at  a  dull  red  heat 
to  constant  weight.  Weigh  0.5  gram  of  the  anhydrous  powder. 
Put  this  in  a  platinum  crucible  with  5  grams  of  pure  potassium 
bisulfate.  Melt  cautiously  and  keep  at  a  low  red  heat  from  five 
to  ten  minutes  until  the  TiO2  all  dissolves  and  the  liquid  becomes 
clear.  Partially  cool  the  crucible  and  add  5  c.c.  of  concentrated 
H2SO4,  then  heat  again  till  the  mass  liquefies.  Cool,  and  put  the 
crucible  and  contents  into  200  to  300  c.c.  of  water  containing 
5  per  cent,  of  H2SO4.  When  the  fusion  is  dissolved,  wash 
and  remove  the  crucible.  The  TiO2  should  dissolve  to  a  clear 
solution.  If  any  residue  remains,  filter  it  out,  wash  and  weigh 
it  and  deduct  it  from  the  Ti02  taken,  using  the  difference  in 
calculating  the  standard  of  the  solution.  Finally  dilute  the  solu- 
tion with  5  per  cent.  H2SO4  till  1  c.c.  contains  1  mg.  of  TiO2. 
Che.ck  it  by  precipitating  and  weighing  the  Ti02  from  20  c.c. 
This  can  be  done  by  the  regular  gravimetric  process.  After 
weighing,  the  TiO2  should  be  tested  for  Si02  by  treating  it  with 
a  little  H2SO4  and  HF,  igniting  and  weighing  the  residue.  Any 
loss  will  be  Si02. 

DETERMINATION   OF  TITANIUM  BY  PRECIPITATION  FROM  ACID 

SOLUTION 

The  following  method  is  adapted  from  the  method  of  Blair.  It 
depends  upon  the  fact  that  when  a  dilute,  slightly  acid  solution  of 
titanium  is  boiled  the  titanium  is  precipitated  by  hydrolysis,  thus 
Ti(S04)2+4HOH  =  Ti(OH)4+2H2S04.  If  the  iron  is  all  present  as 
ferrous  iron  it  does  not  precipitate.  Aluminum  if  present  precipitates 
by  hydrolysis  at  least  partially.  The  titanium  precipitates  quickly 
and  has  no  tendency  to  run  through  the  filter.  It  is  apt  to  be  impure 
and  to  require  a  second  precipitation.  Small  amounts  should  be  finally 
determined  colorimetrically  by  hydrogen  peroxide. 

If  the  sample  contains  much  phosphorus  it  will  prevent  the  precipita- 
tion of  the  titanic  acid  from  an  acid  solution.  Hence  the  phosphorus 
is  first  removed  by  a  sodium  carbonate  fusion. 

Process  of  Analysis. — Dissolve  1  gram  or  more  of  the  iron  or 
steel  in  25  c.c.  of  1:1  nitric  acid.  When  solution  is  complete 
dilute  to  100  c.c.  and  add  NH4OH  until  the  solution  is  alkaline. 
Boil,  let  settle  and  filter  without  washing.  Suck  the  precipitate 


170  METALLURGICAL  ANALYSIS 

as  dry  as  possible,  dry  the  paper  and  contents  in  an  oven  and 
crumble  the  precipitate  out  into  a  mortar.  Burn  the  paper  and 
add  the  ash  to  the  rest  of  the  dried  precipitate.  Grind  the  pre- 
cipitate with  8  grams  of  sodium  carbonate  and  a  little  niter  and 
put  the  mixture  in  a  platinum  crucible.  Fuse  the  mass  and 
keep  fused  a  half  hour,  cool,  dissolve  in  hot  water,  filter  from 
the  insoluble  ferric  oxide,  and  wash  thoroughly  with  hot  water. 
Sodium  silicate,  sodium  phosphate  and  sodium  aluminate  go  in 
the  filtrate.  The  titanium  is  left  on  the  paper  as  sodium  titanate 
with  the  ferric  oxide.  Dry  this  residue,  transfer  it  to  a  large 
platinum  crucible,  preferably  the  one  in  which  the  sodium  car- 
bonate fusion  was  made,  burn  the  filter,  add  its  ash  to  the  residue, 
and  fuse  the  whole  with  fifteen  or  twenty  times  its  weight  of 
potassium  bisulfate.  In  fusing  with  potassium  bisulfate  it  is 
necessary  to  begin  with  a  very  low  heat,  and  to  raise  the  tempe.ra- 
ture  very  slowly  and  carefully  to  a  low  red  heat,  as  the  mixture 
has  a  strong  tendency  to  boil  over  the  top  of  the  crucible  when- 
ever the  temperature  is  increased  too  rapidly.  When  the  lid  of 
the  crucible  is  raised,  fumes  of  sulfuric  anhydride  should  come 
off,  and  the  fusion  should  be  kept  at  this  point  for  several  hours, 
or  until  it  is  quite  clear  and  the  whole  of  the  ferric  oxide  has  been 
dissolved.  Allow  the  fused  mass  to  cool,  add  to  it  from  10  c.c. 
to  20  c.c.  of  strong  sulfuric  acid,  and  heat  until  it  is  perfectly 
liquid.  When  cold  it  will  remain  liquid.  Pour  it  carefully  into 
400  c.c.  of  cold  water  in  a  600  c.c.  beaker.  Add  a  little  hydro- 
chloric acid  if  necessary  and  50  c.c.  of  strong  sulfurous  acid,  or 
5  c.c.  of  ammonium  bisulfite.  Filter  into  an  800  c.c.  beaker,  add 
NH4OH  until  a  permanent  precipitate  forms,  redissolve  with  a 
few  drops  of  hydrochloric  acid,  then  test  a  drop  with  a  drop  of 
KCNS  to  see  if  all  iron  is  reduced.  If  not,  add  a  few  grams  of 
Na2S2O3  and  heat.  Add  a  filtered  solution  of  20  grams  of  sodium 
acetate  and  one-sixth  the  volume  of  the  solution  of  acetic  acid 
(1.04  sp.  gr.),  and  heat  to  boiling.  The  titanic  acid  is  precipi- 
tated almost  immediately  in  a  flocculent  condition  and  quite  free 
from  iron.  Boil  for  a  few  minutes,  allow  the  titanic  acid  to 
settle,  filter  and  wash  with  hot  water  containing  a  little  acetic 
acid.  Dry,  ignite,  and  weigh  as  TiO2  which  contains  60  per  cent, 
titanium.  Should  the  precipitate  contain  an  appreciable  amount 
of  ferric  oxide,  fuse  with  bisulfate  and  reprecipitate.  If  the 


THE  DETERMINATION  OF  TITANIUM  171 

amount  of  titanium  is  under  1  per  cent.,  it  is  best  to  fuse  the  pre- 
cipitate of  Ti02  first  obtained  and  determine  the  titanium 
colorimetrically  as  described  on  page  167. 

Ores  are  fused  directly  with  sodium  carbonate  without  previous 
treatment  with  acid,  and  then  treated  as  above.  The  precipitate 
of  Ti(OH)4  will,  however,  be  apt  to  contain  aluminum  hydroxide 
and  the  titanium  should  either  be  determined  colorimetrically 
or  again  fused  with  sodium  carbonate  and  the  sodium  titanate 
fused  with  bisulfate  and  again  precipitated. 

If  the  ore  contains  zirconium  it  will  prevent  the  precipitation 
of  titanium  from  an  acid  solution.  It  stays  with  the  titanium 
after  the  carbonate  fusion.  Hence  the  best  way  is  probably  to 
precipitate  both  by  the  alkaline  cyanide  method  and  determine 
the  titanium  colorimetrically. 

REFERENCES: 

BLAIR,  "The  Chemical  Analysis  of  Iron,"  seventh  edition,  p.  184. 
HILLEBRAND,  Bulletin,  U.  S.  G.  S.,  p.  128. 
BASKERVILLE,  J.  Soc.  Chem.  Ind.,  1900,  p.  419. 

BUREAU  OF  STANDARDS  METHOD 

When  an  iron  is  dissolved  in  hydrochloric  acid  of  sp.  gr.  1.10, 
all  but  a  trace  of  the  titanium  remains  undissolved.  The  follow- 
ing method  is  based  on  this  fact. 

Dissolve  5  grams  of  the  sample  in  40  c.c.  of  hydrochloric  acid  of 
1.10  sp.  gr.  Filter  off  the  insoluble  matter,  wash  with  water  and 
ignite  the  residue  in  a  platinum  crucible.  Add  a  few  cubic  centi- 
meters of  hydrofluoric  acid  and  several  drops  of  sulfuric  acid 
and  evaporate  to  dryness  and  heat  to  expel  all  the  fluorine.  Add 
several  grams  of  KHSO4  and  fuse  until  everything  is  in  solution, 
keeping  the  fusion  at  a  red  heat.  Cool  and  dissolve  the  cake  in 
water  containing  5  c.c.  of  sulfuric  acid.  Determine  the  titanium 
in  the  solution  colorimetrically. 


CHAPTER  XIV 

THE  DETERMINATION  OF  COPPER  IN  IRON  AND  STEEL 

When  iron  is  dissolved  in  dilute  sulfuric  or  hydrochloric  acid  in  the 
absence  of  oxygen  the  copper  remains  behind  undissolved.  Any  traces 
of  copper  that  dissolve  are  removed  from  solution  by  hydrogen  sulfide. 

Process  of  Analysis. — Dissolve  10  grams  of  sample  in  400  c.c. 
of  10  per  cent,  sulfuric  acid  in  a  large  Erlenmeyer  flask.  When 
dissolved  pass  in  H2S  until  the  solution  is  saturated  with  it, 
filter  and  wash  with  H2S  water.  Burn  the  paper  in  a  porcelain 
crucible,  cool  and  add  to  the  residue  in  the  crucible  5  c.c.  of 
strong  HNO3  and  heat  until  the  copper  oxide  is  all  dissolved. 
Dilute,  add  7  c.c.  of  NH4OH,  filter  if  necessary  into  a  100  c.c. 
Nessler  tube  and  wash  with  water.  If  there  is  any  copper  present 
the  alkaline  filtrate  will  be  blue. 

To  another  Nessler  tube  add  about  50  c.c.  of  water,  5  c.c.  of 
nitric  acid  and  7  c.c.  of  NH4OH.  Add  from  a  burette  a  standard 
copper  nitrate  solution  until  the  color  in  the  two  tubes  is  exactly 
the  same. 

The  dilution  and  temperature  of  the  two  solutions  should  be 
about  the  same. 

If  the  amount  of  copper  in  the  sample  is  too  low  to  be  easily 
seen  in  the  alkaline  solution,  add  1  c.c.  of  a  1  per  cent,  solution 
of  potassium  ferrocyanide  and  then  sufficient  dilute  sulfuric  acid 
to  make  the  solution  slightly  acid.  A  coppery  color  of  copper 
ferrocyanide  will  appear  if  there  is  the  slightest  amount  of  copper 
present.  Treat  the  other  tube  the  same  way  and  add  the  stand- 
ard solution  until  the  colors  are  the  same. 

Make  the  standard  solution  by  dissolving  3.928  grams  of 
CuSO4,  5H2O  in  water  and  diluting  to  1  liter.  One  cubic  centi- 
meter contains  0.001  gram  of  copper. 

Instead  of  determining  the  copper  colorimetrically  it  may  be 
determined  in  the  final  nitric  acid  solution  electrolytically  or  by 
the  iodine  method. 

172 


CHAPTER  XV 
DETERMINATION  OF  ARSENIC  IN  IRON  AND  STEEL 

This  element  may  be  estimated  by  dissolving  10  grams  of  the  metal 
in  HN03,  sp.  gr.  1.2,  evaporating  and  baking  as  for  phosphorus,  dis- 
solving the  residue  in  concentrated  HC1  without  heating,  which  might 
volatilize  AsCl3,  diluting,  reducing  with  Na2S03  and  precipitating  with 
H2S  as  As2S3.  The  As2S3  is  then  oxidized  by  fuming  HN03,  precipi- 
tated with  magnesia  mixture  and  weighed  as  Mg2As207.  For  details, 
see  Fresenius'  Quantitative  Analysis. 

The  following  method  is  much  shorter  and  is  sufficiently  accurate  when 
only  small  percentages  are  present.  It  depends  upon  the  volatiliza- 
tion of  As  as  AsCl3  when  a  solution  containing  it  is  boiled  with  HC1  and 
a  large  excess  of  ferric  and  ferrous  chloride.  In  order  that  the  volatiliza- 
tion may  be  rapid  and  complete,  the  liquid  should  have  its  boiling-point 
raised  to  about  108°C.  by  the  addition  of  ZnCl2,  or  CaCl2,  and  should 
contain  concentrated  HC1. 

Process  of  Analysis. — Arrange  the  flask  as  for  the  evolution 
sulfur  method.  The  delivery  tube  must  have  a  couple  of  bulbs 
of  2  c.c.  capacity  in  it  to  catch  any  FeCl3  mechanically  carried 
over.  The  test-tube  receiving  the  vapors  should  stand  in  a'  large 
beaker  of  cold  water. 

Dissolve  100  grams  of  commercial  FeCl3  in  150  c.c.  of  concen- 
trated HC1  in  a  500  c.c.  beaker.  Gentle  warming  accelerates 
the  solution.  When  dissolved,  add  cautiously  4  grams  of  pul- 
verized zinc.  When  this  is  dissolved,  boil  the  solution  gently 
for  10  minutes  to  expel  the  traces  of  arsenic  found  in  the  reagents. 
With  new  chemicals  it  is  well  to  do  this  boiling  in  the  flask,  as  in 
the  regular  determination,  and  determine  the  arsenic  given  off. 
If  this  is  more  than  a  trace,  get  other  reagents.  After  boiling, 
cool  the  mixture.  Weigh  into  the  empty  evolution  flask  10 
grams  of  the  metal  to  be  tested.  Put  100  c.c.  of  cold  water  into 
the  large  test-tube  into  which  the  delivery  tube  dips.  Now  add 
the  FeCl3  mixture  through  the  funnel  tube,  running  it  in  very 
cautiously  to  avoid  violent  action.  It  may  take  8  to  10  min- 

173 


174  METALLURGICAL  ANALYSIS 

utes  to  do  this.  Warm  if  necessary  until  the  iron  is  dissolved; 
then  heat  to  boiling  and  boil  steadily  for  15  minutes  The 
arsenic  will  practically  all  distill  over  as  AsCl3  and  condense  in 
the  water  in  the  test-tube.  The  delivery  tube  should  pass  to  the 
bottom  of  this  tube  and  the  water  in  the  beaker  in  which  the 
test-tube  is  placed  be  kept  cold,  as  the  liquid  in  the  tube  must  not 
be  allowed  to  reach  the  boiling-point.  At  the  end  of  15  minutes 
take  out  the  test-tube  and  substitute  a  second  one  containing  a 
similar  amount  of  water,  and  boil  the  solution  10  minutes  longer. 
The  second  tube  should  show  no  more  than  a  trace  of  arsenic. 

The  liquid  in  the  tube  is  poured  into  a  beaker,  and  if  not 
strongly  acid  is  made  so  by  adding  HC1,  heated  to  near  the  boil- 
ing-point and  precipitated  by  a  rapid  current  of  H2S.  The 
As2S3  will  separate  promptly  and  may  be  filtered  off  on  a  small 
weighed  filter,  washed  first  with  water,  then  twice  with  absolute 
alcohol,  then  with  pure  bisulfide  of  carbon  to  remove  any  sulfur 
present.  Dry  the  precipitate  at  100°C.  and  weigh. 

The  arsenic  may  be  determined  volumetrically  as  follows: 
Pour  into  a  beaker  the  liquid  from  the  tube  into  which  the  ar- 
senic was  distilled  and  cool  it.  Add  a  solution  of  sodium  bicar- 
bonate (NaHCO3)  until  the  acid  is  all  neutralized,  then  add  1 
c.c.  of  5  per  cent,  solution  in  excess.  Add  starch  paste  and  ti- 
trate with  standard  iodine  such  as  is  used  for  arsenic  on  page 
225.  The  reaction  is,  AsCl8+ 4H2O+2I  =  H3AsO4+2HH-3HCL 
The  acid  liberated  is  neutralized  by  the  sodium  bicarbonate 
present.  Normal  sodium  carbonate  or  hydroxide  must  not  be 
used. 

Since  one  atom  of  sulfur  as  H2S  requires  two  atoms  of  iodine 
and  one  atom  of  arsenic  requires  two  atoms  of  iodine,  one  atom  of 
sulfur  is  equal  to  one  of  arsenic  and  the  sulfur  value  of  the  iodine 
multiplied  by  1%2  gives  the  arsenic  value  of  the  iodine. 

A  black  insoluble  residue  left  when  the  iron  is  dissolved  there 
may  contain  arsenic.  In  such  a  case  it  is  best  to  dissolve  the 
sample  in  1:1  nitric  acid,  add  20  c.c.  of  sulfuric  acid,  heat  to 
strong  fumes  and  continue  the  heating  until  the  excess  of  sulfuric 
acid  is  driven  off.  Cool,  transfer  the  residue  to  a  distilling  flask, 
add  the  ferrous  chloride  solution  and  proceed  as  usual. 

It  is  absolutely  necessary  to  run  a  blank  on  the  reagents  and  subtract 
the  blank  titration  from  the  regular  titration. 


DETERMINATION  OF  ARSENIC  IN  IRON  AND  STEEL    175 

REFERENCES: 

GIBB,  J.  Soc.  Chem.  Ind.,  1901,  p.  184. 
NORRIS,  /.  Soc.  Chem.  Ind.,  1902,  p.  393. 
BLAIR,  "The  Chemical  Analysis  of  Iron,"  p.  201. 
STEAD,  J.  Iron  and  Steel  Inst.}  1895,  I. 


CHAPTER  XVI 

THE  DETERMINATION  OF  ALUMINIUM  IN  IRON  AND 

STEEL 

Stead's  Method.— J.  Soc.  Chem.  Ind.,  1889,  p.  965.  This  depends 
upon  the  complete  precipitation  of  aluminium  as  phosphate  in  the 
presence  of  sodium  phosphate  in  boiling  solutions  containing  an  excess 
of  sodium  thiosulfate.  Acetic  acid  and  acetates  do  not  interfere.  Iron 
in  the  ferric  state  must  be  absent.  Ferrous  iron  does  not  interfere. 
The  excess  of  thiosulfate  rapidly  reduces  the  ferric  iron  at  a  boiling  heat. 

Process  of  Analysis. — Dissolve  11  or  22  grams  of  the  metal, 
according  to  the  percentage  of  aluminium  in  44  or  88  c.c.  of 
concentrated  HC1.  Evaporate  to  dryness  to  separate  SiO2. 
Take  up  in  HC1  and  filter.  Dilute  the  filtrate  to  200  c.c.,  add  3 
c.c.  of  a  saturated  solution  of  Na2HPO4,  then  NH4OH  till  a  slight 
permanent  precipitate  appears.  Dissolve  this  by  adding  HC1 
drop  by  drop.  Heat  to  boiling  and  add  50  c.c.  of  a  saturated 
solution  of  sodium  thiosulfate.  Now  boil  gently  till  all  the  SO2  is 
expelled,  which  will  usually  take  about  half  an  hour.  Filter  off 
the  precipitate  rapidly,  using  a  larger  filter,  and  wash  it  thoroughly 
with  hot  water.  The  precipitate  consists  of  sulfur,  aluminium 
phosphate  and  a  little  iron.  Wash  the  precipitate  back  into  the 
beaker.  Let  it  settle  and  decant  off  the  excess  of  water  through 
the  filter.  To  the  remainder  in  the  beaker,  which  should  not  ex- 
ceed 5  or  6  c.c. ,  add  an  equal  volume  of  concentrated  HC1  and 
warm  to  nearly  boiling,  stirring  it  thoroughly.  Now  filter  the 
solution  through  the  same  filter  into  a  platinum  dish,  washing  filter 
and  precipitate  thoroughly.  Evaporate  this  solution  containing 
the  aluminium  phosphate  to  dryness.  The  residue  on  the  filter 
is  sulfur  and  may  be  rejected.  It  is  well  to  burn  it,  however, 
and  examine  any  residue  for  aluminium.  To  the  dry  residue  in 
the  platinum  dish  add  2  grams  of  pure  NaOH  (from  sodium)  and 
1  c.c.  of  water.  Heat  till  the  sodium  hydrate  dissolves,  and  then 
stir  the  residue  thoroughly  into  it.  Cool,  add  water  and  boil 

176 


DETERMINATION  OF  ALUMINIUM  IN  IRON  AND  STEEL  177 

five  minutes.  Transfer  the  turbid  solution  to  a  flask  and  dilute 
to  110  c.c.  Filter  through  a  dry  filter  and  collect  100  c.c.  of  the 
filtrate,  equivalent  to  10  or  20  grams  of  the  steel,  according  to  the 
amount  taken.  Neutralize  with  HC1  in  slight  excess.  Add  3  c.c. 
of  Na2HPO4  solution  and  again  precipitate  by  adding  10  c.c. 
sodium  thiosulfate  and  boiling.  After  the  precipitate  is  formed 
and  the  SO 2  expelled,  add  2  or  3  c.c.  of  a  saturated  solution  of 
ammonium  acetate.  Boil  two  minutes  longer  and  filter.  Wash 
with  hot  water  till  free  from  chlorine.  Burn  off,  ignite,  and 
weigh  as  A1PO4,  which  contains  22.18  per  cent,  of  aluminium. 
Run  a  blank  on  all  the  reagents  used  and  make  a  correction  for 
any  A12O3  or  SiO2  so  found.  If  chromium  is  present,  it  will  be  in 
part  precipitated  with  the  aluminium.  Its  presence  will  be 
shown  by  the  yellow  color  it  gives  to  the  soda  fusion.  It  can  be 
removed  by  adding  a  few  drops  of  an  alkaline  sulfite  to  this  solu- 
tion and  boiling  for  some  time;  the  CrO3  will  be  reduced  and 
precipitated.  If  the  sample  contains  any  titanium  it  will  be  pre- 
cipitated with  the  aluminium  and  should  be  determined  colori- 
metrically  in  the  precipitate. 

ETHER  METHOD 

When  the  ether  separation  as  given  on  page  155  is  carried  out,  the 
aluminium  passes  into  the  aqueous  solution  with  vanadium,  manganese, 
nickel,  etc.  The  aluminium  can  then  be  precipitated  as  above  without 
having  such  a  large  amount  of  iron  present. 

Process. — Treat  a  5  or  10  gram  sample  as  directed  on  page  155 
until  the  aqueous  solution  is  separated  from  the  ethereal  solution. 
Then  add  2  c.c.  H2S04,  evaporate  the  solution  until  fumes  of 
H2SO4  appear,  dilute  to  50  c.c.  and  precipitate  the  aluminium  as 
directed  above  for  the  second  precipitation. 

See  also  phenylhydrazine  method  on  page  309. 


12 


CHAPTER  XVII 
THE  DETERMINATION  OF  NITROGEN  IN  STEEL 

The  presence  of  much  nitrogen  in  steel  is  said  to  be  very  harmful  to 
the  steel.  Hence  the  determination  of  it  becomes  of  importance  at 
times. 

The  following  method  is  the  one  devised  by  Allen  and  perfected  by 
Langley  as  it  is  used  by  the  American  Rolling  Mills  Co.  It  depends 
upon  the  fact  that  when  a  steel  is  dissolved  in  hydrochloric  acid  the 
nitrogen  which  was  present  as  nitride  is  retained  by  the  acid  present 
as  ammonium  chloride.  The  solution  is  then  made  alkaline  by  sodium 
hydroxide  and  the  ammonia  distilled  off.  The  distilled  ammonia  is 
then  treated  with  Nessler's  reagent  with  which  it  produces  a  brown  pre- 
cipitate of  enormous  coloring  power,  so  that  the  minutest  trace  of  am- 
monia can  be  recognized  by  the  formation  of  a  distinct  yellow  color. 
The  reaction  is 

2HgK2l4+3KOH+NH4OH  =  3H20+7KI+OHg2NH2I 

the  mercury  compound  being  the  colored  precipitate. 

Since  the  reaction  is  so  very  delicate  the  utmost  care  must  be  used  to 
see  that  no  ammonia  is  allowed  to  get  into  the  solutions  used  from  the  air 
and  especially  prepared  water  and  chemicals  must  be  used.  Even  then 
it  is  imperative  that  blanks  be  frequently  run.  The  determination  must 
be  made  in  a  room  in  which  there  is  no  (or  the  least  possible)  quantity  of 
free  ammonia  or  ammonium  salts  in  the  air. 

The  reagents  required  are: 

Hydrochloric  Acid  of  1 : 1  Specific  Gravity,  Free  from  Am- 
monia.— This  may  be  prepared  by  distilling  pure  hydrochloric 
acid  gas  into  distilled  water  free  from  ammonia.  To  do  this, 
take  a  large  flask  fitted  with  a  rubber  stopper  carrying  a  sepa- 
ratory  funnel  tube  and  an  evolution  tube.  Place  in  the  flask 
strong  hydrochloric  acid,  connect  the  evolution  tube  with  a  wash 
bottle  connected  with  a  bottle  containing  the  distilled  water. 
Admit  strong  sulfuric  acid  free  from  nitrous  acid  to  the  flask 
through  the  funnel  tube,  apply  heat  as  required,  and  distill  the 
gas  into  the  prepared  water. 

178 


DETERMINATION  OF  NITROGEN  IN  STEEL  179 

Test  the  acid  by  admitting  some  of  it  into  the  distilling  appa- 
ratus, described  further  on,  and  distilling  it  from  an  excess  of 
pure  caustic  soda,  or  determine  the  amount  of  ammonia  in  a  por- 
tion of  hydrochloric  acid  of  1  : 1  specific  gravity,  and  use  the 
amount  found  as  a  correction. 

Solution  of  Caustic  Soda. — Dissolve  300  grams  of  fused  caustic 
soda  in  500  c.c.  of  water,  and  digest  it  for  24  hours  at  50°C.  with 
a  copper-zinc  couple  prepared  by  rolling  together  about  6  sq.  in. 
each  of  zinc  and  copper  foil. 

Nessler  Reagent. — Dissolve  35  grams  of  potassium  iodide  in  a 
small  quantity  of  distilled  water,  and  add  a  strong  solution  of 
mercuric  chloride  little  by  little,  shaking  after  each  addition, 
until  the  red  precipitate  dissolves.  Finally  the  precipitate 
formed  will  fail  to  dissolve :  then  stop  the  addition  of  the  mercury 
salt  and  filter.  Add  to  the  filtrate  120  grams  of  caustic  soda 
dissolved  in  a  small  amount  of  water,  .and  dilute  until  the  entire 
solution  measures  1  liter.  Add  to  this  5  c.c.  of  saturated  aqueous 
solution  of  mercuric  chloride,  mix  thoroughly,  allow  the  precipi- 
tate formed  to  settle  and  decant  or  siphon  off  the  clear  liquid  into 
a  glass-stoppered  bottle. 

Standard  Ammonia  Solution. — Dissolve  0.0382  gram  of  am- 
monium chloride  in  1  liter  of  water;  1  c.c.  of  this  solution  will 
equal  0.01  mg.  of  nitrogen. 

Distilled  Water  free  from  Ammonia. — If  the  ordinary  distilled 
water  contains  ammonia,  redistill  it,  reject  the  first  portions 
coming  over,  and  use  the  subsequent  portions,  which  will  be  found 
free  from  ammonia.  Several  glass  cylinders  of  colorless  glass  of 
about  160  c.c.  capacity  are  required. 

The  best  form  of  distilling  apparatus  consists  of  an  Erlenmeyer 
flask  of  about  1500  c.c.  capacity,  with  a  rubber  stopper  carrying 
a  separatory  funnel  tube  and  an  evolution  tube,  the  latter  con- 
nected with  a  condensing  tube,  around  which  passes  a  constant 
stream  of  cold  water.  The  inside  tube  where  it  issues  from  the 
condenser  should  be  sufficiently  high  to  dip  into  one  of  the  glass 
cylinders  placed  on  the  working  table. 

Process  of  Analysis. — Place  40  c.c.  of  the  caustic  soda,  which 
has  been  treated  with  the  copper-zinc  couple,  in  the  Erlenmeyer 
flask,  add  500  c.c.  of  -water  and  about  25  grams  of  tin-foil  to 
prevent  bumping,  and  distill  until  the  distillate  gives  no  reaction 


180  METALLURGICAL  ANALYSIS 

with  the  Nessler  reagent.  While  this  part  of  the  operation  is  in 
progress  dissolve  3  grams  of  the  carefully  washed  drillings  in  30 
c.c.  of  the  prepared  hydrochloric  acid,  using  heat  if  necessary. 
Transfer  the  solution  to  the  bulb  of  the  separatory  funnel  tube, 
and  when  the  soda  solution  is  free  from  ammonia,  very  slowly 
drop  the  ferrous  chloride  solution  into  the  boiling  solution  in  the 
flask  until  it  is  all  in.  Heat  to  boiling.  When  about  50  c.c.  of 
water  has  been  collected  in  the  cylinder,  remove  it  and  substitute 
another  cylinder.  Place  1J^  c.c.  of  the  Nessler  reagent  in  a 
cylinder,  dilute  the  distillate  to  100  c.c.  with  the  special  distilled 
water  and  pour  it  into  the  cylinder  containing  the  Nessler  reagent. 
Take  another  cylinder,  place  therein  1^  c.c.  of  the  Nessler 
reagent  and  100  c.c.  of  the  special  distilled  water  to  which  1  c.c. 
of  the  ammonium  chloride  solution  has  been  added,  and  compare 
the  colors  of  the  solutions  in  the  two  cylinders.  If  the  solution  in 
the  cylinder  containing  the  ammonium  chloride  solution  is  lighter 
in  color  than  that  in  the  cylinder  containing  the  distillate,  place 
1%  c.c.  of  the  Nessler  reagent  in  another  cylinder,  pour  into  it 
100  c.c.  of  water  containing  2  or  more  cubic  centimeters  of  the 
ammonium  chloride  solution,  and  repeat  this  operation  until  the 
colors  of  the  solutions  in  the  two  cylinders  correspond  after 
standing  about  ten  minutes.  When  about  100  c.c.  have  distilled 
into  the  second  cylinder,  replace  it  and  test  as  before.  Continue 
the  distillation  until  the  water  comes  over  free  from  ammonia, 
then  add  together  the  number  of  cubic  centimeters  of  ammonia 
solution  used,  divide  the  sum  by  3,  and  each  0.01  mg.  will  be 
equal  to  0.001  per  cent,  of  nitrogen  in  the  steel. 


CHAPTER  XVIII 
THE  DETERMINATION  OF  OXYGEN  IN  STEEL 

This  important  determination  has  not  received  as  much  attention  as 
it  should  have,  as  the  properties  of  steel  are  considerably  affected  by 
the  presence  of  considerable  amounts  of  oxygen.  The  oxygen  exists 
in  the  steel  as  oxides  of  iron,  manganese,  silicon,  titanium,  aluminum, 
etc.  The  method  here  given  depends  upon  the  reaction  between  the 
oxide  of  iron  and  hydrogen  at  a  high  temperature  with  the  formation  of 
water  vapor  which  is  absorbed  in  phosphorus  pentoxide  and  weighed. 

Since  hydrogen  does  not  reduce  the  oxides  of  manganese,  aluminum, 
and  silicon,  the  oxides  combined  with  them  are  not  determined  with  this 
method,  that  is,  the  method  determines  only  the  occluded  oxygen  and 
the  oxygen  combined  with  the  iron  and  other  easily  reduced  metals. 
However,  when  the  metal  is  a  very  pure  iron  containing  only  a  few 
hundredths  per  cent,  of  manganese  and  a  trace  of  silicon  the  result  for 
oxygen  obtained  by  this  method  must  be  fairly  accurate.  It  is  pre- 
cisely in  this  kind  of  iron  that  the  oxygen  content  must  be  closely 
watched. 

The  following  method  is  the  one  of  Ledebur  as  given  by  Cushman.1 
The  writer  is  indebted  to  the  American  Rolling  Mills  Co.,  for  the  details. 

A  number  of  other  methods  for  the  determination  of  oxygen  have  been 
proposed,  among  which  may  be  mentioned:  (1)  Heating  the  sample  in  a 
stream  of  dry  chlorine;  (2)  dissolving  the  sample  in  special  solvents 
such  as  copper  or  bromine. 

In  Ledebur's  original  method  the  sample  is  given  a  preliminary 
heating  in  pure  nitrogen  in  order  to  burn  the  last  traces  of  impurities 
and  to  get  rid  of  all  hydrocarbons.  If  the  preliminary  heating  in  nitro- 
gen is  dispensed  with,  the  results  will  be  slightly  higher,  but  it  is  probable 
that  for  general  work  sufficiently  accurate  results  can  be  obtained  if 
the  sample  is  carefully  prepared  for  the  combustion  in  hydrogen. 

Samples. — The  samples  should  consist  of  fine  borings  or  shav- 
ings from  a  milling  machine.  The  drillings  should  be  taken  from 
many  parts  of  the  ingot  as  FeO  segregates  badly.  The  drill  or 

1  CUSHMAN,  J.  Ind.  Eng.  Chem.,  June,  1911. 

181 


182 


METALLURGICAL  ANALYSIS 


machine  tool  should  be  scrupulously  clean  and  free  from  all 
traces  of  oil  or  dirt,  and  should  be  geared  to  run  slowly  so  as 
not  to  heat  the  sample  while  it  is  being  cut.  Lack  of  careful 
attention  to  this  point  will  lead  to  high  results  owing  to  surface 
oxidation  of  the  fine  particles  of  the  drillings.  The  drillings 
should  be  dried  in  a  desiccator. 

Apparatus. — The  apparatus  used  in  making  the  oxygen  deter- 
mination is  shown  in  Fig.  11. 

A  4  liter  Kipp  generator  is  used  for  generating  the  hydrogen. 
It  should  be  charged  with  drillings  of  pure  iron  or  mossy  zinc, 
and  dilute  hydrochloric  acid  (1:1).  Steel  turnings  should  not 
be  used  in  the  generator,  as  the  object  is  to  generate  the  purest 


FIG.  11. 

possible  hydrogen.  Hydrochloric  is  preferable  to  sulfuric  acid. 
After  its  formation  the  hydrogen  is  purified  and  dried  by  passing 
through  the  usual  train  as  shown  in  the  figure.  It  passes  first 
over  stick  potash,  and  next  through  a  30  per  cent,  potash  solu- 
tion. This  solution  in  the  second  bottle  should  be  renewed  as 
soon  as  it  shows  a  tinge  of  yellow  due  to  the  presence  of  sulfides. 
The  hydrogen  next  passes  through  concentrated  sulfuric  acid 
to  dry  it,  and  then  enters  a  silica  tube  with  J£  m-  bore,  30  in.  in 
length,  which  contains  a  roll  of  platinum  gauze  or  palladiumized 
asbestos.  The  Y±  in.  tube  lies  on  top  of  a  1  in.  X  30  in.  fused 
silica  tube  contained  in  a  suitable  12-in.  gas  blast  furnace.  It 
is  better  to  preheat  the  hydrogen  in  a  separate  furnace. 


DETERMINATION  OF  OXYGEN  IN  STEEL  183 

The  object  of  the  preliminary  heating  over  platinum  foil  is 
to  free  the  hydrogen  from  the  small  quantity  of  oxygen  which  It 
always  contains.  If  this  precaution  is  not  taken,  the  results  will 
be  too  high.  The  water  formed  in  the  small-bore  tube  is  caught 
in  a  U-tube  shown  in  the  figure,  which  contains  phosphoric 
anhydride  opened  up  with  glass  wool.  This  drying  tube  has 
rubber  stoppers.  The  connection  is  made  with  pure  gum  tub- 
ing and  is  permanent,  the  sample  being  introduced  from  the 
opposite  end  of  the  combustion  tube.  All  rubber  connections 
should  be  made  tight  as  directed  on  page  277. 

Blanks  should  be  run  from  time  to  time  to  make  sure  that  the 
apparatus  is  in  good  order  and  everything  working  properly. 
Samples  should  not  be  introduced  into  or  removed  from  the  com- 
bustion tube  when  it  is  more  than  hand  hot,  but  silica  tubes  may 
be  quickly  cooled  with  perfect  safety  by  turning  off  the  gas  and 
allowing  the  cold  air  blast  to  play  on  the  tube. 

Process  of  Analysis. — Weigh  20  to  30  grams  of  finely  divided 
borings  into  a  nickel  boat  Y^  in.  X  M  m-  X  6  in.  The  boat 
with  its  charge  is  quickly  inserted  into  the  combustion  tube  at 
the  right  end  and  pushed  to  the  middle  zone  by  means  of  a  rod 
of  suitable  length.  The  stream  of  hydrogen  should  be  passing 
freely  when  the  tube  is  opened  for  the  insertion  of  the  sample. 
After  the  stopper  is  replaced,  the  weighing  tube  and  guard  tube 
are  finally  connected  up  with  pure  gum  tubing.  The  weighing 
tube  is  a  4  in.  U-tube,  with  ground  glass  stoppers,  containing 
phosphoric  anhydride  opened  up  with  glass  wool.  The  guard 
or  trap  tube  is  similarly  charged  and  is  intended  to  prevent  the 
drawing  back  of  moisture  from  the  air  of  the  laboratory.  After 
the  apparatus  is  all  connected  and  in  good  order,  the  pure  dry 
hydrogen  should  be  allowed  to  sweep  through  a  few  minutes 
until  all  air  is  removed  from  the  entire  system.  The  gas  is 
then  lighted,  the  blast  turned  on  and  the  temperature  run  up 
to  a  bright  red  heat,  about  850°C.  This  heat  is  maintained  for 
30  minutes  while  the  hydrogen  is  passing  through  the  apparatus 
at  the  brisk  rate  of  about  100  c.c.  per  minute.  After  the  com- 
bustion is  completed  the  gas  is  turned  off  the  furnace,  leaving 
the  blast  playing  upon  the  hot  tube.  The  stream  of  hydrogen 
should  continue  to  pass  until  the  tube  is  cool  enough  to  bear 
the  hand  upon  it. 


184  METALLURGICAL  ANALYSIS 

Immediately  after  the  tube  is  cool  enough,  the  weighing  tube, 
with  its  guard  tube,  is  disconnected  and  connected  with  a  suit- 
able aspirator,  so  as  to  suck  out  the  hydrogen  gas  and  replace 
it  with  air  dried  over  P2O5.  A  suitable  aspirator  consists  of  a 
4  liter  aspirator  bottle  filled  with  water.  The  upper  tubular 
of  the  bottle  is  guarded  with  a  calcium  chloride  tube  to  which  the 
weighing  tube  is  connected.  A  gas  washing  bottle  containing 
concentrated  sulfuric  acid  follows  the  phosphoric  anhydride 
tube  which  is  connected  to  the  other  side  of  the  weighing  tube. 

Notes  on  the  Process. — The  aspirator  may  be  roughly  calibrated  by 
allowing  about  500  c.c.  of  water  to  run  out  of  the  lower  tubular  of  the 
aspirator.  A  sufficient  quantity  of  perfectly  dry  air  is  drawn  through  to 
thoroughly  displace  all  the  hydrogen.  After  all  is  ready,  the  weighed 
tube  is  closed  by  its  glass  stop-cocks,  disconnected  from  its  guard  tube 
and  placed  in  a  desiccator  for  15  minutes  before  being  weighed.  Eight- 
ninths  of  the  increased  weight  of  the  tube  is  oxygen.  The  blanks  on  the 
apparatus  establish  the  average  correction  to  be  subtracted  from  the 
weight  found.  The  correction  on  an  apparatus  in  good  order  should  not 
exceed  2  mg.  On  damp  days  the  blank  is  usually  a  little  higher  than 
when  the  air  is  dry. 

If  the  stop-cocks  on  the  weighing  tube  are  ground  so  as  to  fit  very 
tightly  it  is  not  necessary  to  displace  the  hydrogen  with  air.  If  the 
cocks  do  not  fit  very  tightly  some  hydrogen  will  diffuse  out. 

In  charging  the  weighing  tube  with  phosphoric  anhydride  and  glass 
wool,  take  care  to  remove  any  specks  of  phosphoric  anhydride  from  the 
upper  portions  of  the  tube. 

The  following  points  should  be  given  careful  attention  in  order  to 
attain  the  highest  degree  of  accuracy: 

Samples  must  be  clean,  absolutely  dry  and  free  from  oil.  They  should 
be  cut,  preferably  with  a  milling  machine  tool  running  at  a  low  rate  of 
speed.  The  samples  must  not  heat  in  cutting.  Sheet  samples  are  first 
cleaned  from  oxide  on  an  emery  wheel,  avoiding  heating  as  much  as 
possible.  The  sheet  should  be  milled  on  the  edge. 

Whenever  possible,  samples  should  be  cut  from  bars  which  are  first 
cleaned  by  a  superficial  cut  with  the  milling  tool.  Extreme  care  must  be 
taken  in  the  preparation  of  the  sample. 

The  entire  apparatus  must  be  kept  to  the  top  notch  of  cleanliness, 
tightness  and  general  good  order.  Blanks  should  be  run  frequently. 
Analyses  should  be  in  duplicate  whenever  the  results  are  to  be  used  as  a 
basis  for  specification.  The  most  extreme  care  should  be  taken  to 
exclude  all  oxygen  from  the  sample  and  apparatus  except  that  which 


DETERMINATION  OF  OXYGEN  IN  STEEL  185 

it  is  the  object  of  the  method  to  determine.  When  determining  oxygen 
in  pure  iron,  the  silver  white  iron  residues  from  the  boat  may  be  reserved 
for  charging  the  Kipp  hydrogen  generator. 

METHOD  FOR  TOTAL  OXYGEN 

This  method  depends  upon  the  reduction  of  the  oxides  by  carbon  in  a 
vacuum  furnace  at  a  very  high  temperature.  The  carbon  monoxide 
formed  is  passed  through  iodine  pentoxide  forming  carbon  dioxide  and 
liberating  iodine  which  is  absorbed  in  potassium  iodide  and  titrated 
with  sodium  thiosulfate.  (See  WALKER  and  PATRICK,  J.  Ind.  Eng. 
Chem.,  Nov.,  1912,  p.  799.) 


CHAPTER  XIX 
DETERMINATION  OF  HYDROGEN  IN  STEEL 

The  following  method  is  the  one  used  by  the  American  Rolling  Mills 
Co. 

Some  of  the  hydrogen  is  liberated  by  drilling,  so  that  it  is  necessary 
to  work  with  the  metal  in  a  single  piece,  if  possible.  However,  if  the 
metal  is  in  strips,  several  can  be  used  for  an  analysis. 

The  method  is  based  on  the  fact  that  hydrogen  is  liberated  by  heating 
the  metal  to  a  red  heat  in  an  atmosphere  of  oxygen.  The  hydrogen  is 
oxidized  to  water,  which  is  absorbed  in  phosphoric  anhydride. 

The  apparatus  used  (Fig.  12)  consists  of  a  12-in.  gas  blast 
furnace  in  which  is  placed  a  30  in.  X%  in.  silica  tube,  and  on 


FIG.  12. 

top  of  this  tube  is  placed  a  30  in.  X  J4  in.  silica  tube.  The 
silica  tubes  each  have  a  6  in.  roll  of  platinum  gauze  or  palladium- 
ized  asbestos  to  act  as  a  catalyzer.  The  oxygen  gas  passes 
through  the  %  m-  silica  tube  (T-2)  at  the  rate  of  100  c.c.  per 
minute,  and  the  impurities  are  thus  oxidized.  The  gas  then 
passes  through  a  wash  bottle  containing  a  strong  solution  of 
caustic  potash  (K— 2),  then  through  a  bottle  containing  stick 
caustic  potash  (K),  then  through  a  bottle  containing  concen- 
trated sulfuric  acid  (S-l),  and  finally  through  a  tube  containing 
phosphoric  anhydride  opened  up  with  glass  wool  (P-l).  The 
purified  oxygen  then  enters  the  %  in.  silica  tube  (T-l),  where 

186 


DETERMINATION  OF  HYDROGEN  IN  STEEL  187 

it  combines  with  the  liberated  hydrogen,  forming  water,  which 
is  swept  into  the  4  in.  glass  stop-cock  U-tube  containing  phos- 
phoric anhydride  opened  up  with  glass  wool  (P-2).  This  tube 
is  weighed  and  connected  with  a  tube  of  phosphoric  anhydride 
opened  up  with  glass  wool  (P-3)  used  as  a  trap.  The  gas 
finally  passes  through  a  solution  of  concentrated  sulfuric  acid, 
which  is  used  to  show  that  the  gas  is  passing  through  the 
apparatus. 

Process  of  Analysis. — The  silica  tubes  should  be  at  a  red  heat 
and  oxygen  should  pass  through  the  apparatus  at  the  rate  of  100 
c.c.  per  minute.  Place  the  sample  in  either  a  clay  boat,  or  one  of 
platinum  containing  ignited  alundum,  in  as  large  pieces  as  are 
available,  using  from  10  to  40  grams  for  a  determination. 

Weigh  U-tube  (P-2)  and  connect  direct  with  stopper  to  % 
in.  silica  tube.  Remove  stopper  and  tube  (P-l)  and  insert  the 
boat  into  the  red-hot  zone  of  the  silica  tube.  Connect  tube 
(P-l)  with  silica  tube  and  continue  passing  the  oxygen  gas 
through  the  apparatus  at  the  rate  of  100  c.c.  per  minute  for  30 
minutes.  At  the  end  of  this  time  disconnect  weighing  tube 
(P-2)  and  connect  with  a  suitable  aspirator,  so  as  to  suck  out 
the  oxygen  and  replace  it  with  dry  air.  A  suitable  aspirator 
consists  of  a  4  liter  aspirator  bottle  filled  with  water.  The 
upper  tubular  is  guarded  with  a  calcium  chloride  tube  to  which 
the  weighing  tubes  are  connected,  and  the  other  side  of  weighing 
tube  is  connected  with  a  phosphoric  anhydride  tube  followed  by  a 
washing  bottle  containing  concentrated  sulfuric  acid. 

The  aspirator  may  be  roughly  calibrated  by  allowing  500  c.c. 
of  water  to  run  out  of  the  lower  tubular  of  the  aspirator.  This 
is  a  sufficient  amount  of  dry  air  to  thoroughly  displace  all  the 
oxygen. 

The  glass  stop-cocks  of  the  weighing  tube  are  now  closed  and 
weighing  tube  disconnected  from  the  guard  tube  and  placed  in  a 
desiccator  for  15  minutes  before  being  weighed.  One-ninth  of 
the  increased  weight  of  the  tube  is  hydrogen. 

Notes  on  the  Process. — It  is  absolutely  necessary  to  run  a  blank  deter- 
mination using  the  same  amount  of  oxygen  as  for  a  regular  test,  and  it 
must  also  be  run  for  the  same  length  of  time.  The  blank  should  never 
exceed  1  mg.  This  blank  is  derived  from  the  oxidation  of  the  rubber 


188  METALLURGICAL  ANALYSIS 

connections,  hence  the  necessity  for  using  a  definite  amount  of  oxygen 
for  a  definite  length  of  time. 

In  charging  the  weighing  tube  with  phosphoric  anhydride,  take 
about  a  gram  on  glass  wool,  fold  the  glass  wool  over  the  phosphoric  acid 
and  insert  into  the  tube.  Repeat  until  the  tube  is  full.  Use  great  care 
to  remove  all  specks  of  phosphoric  anhydride  from  the  inlet  and  exit 
tubes  of  weighing  tube. 

The  temperature  of  the  silica  tubes  must  be  regulated  so  that  the  sam- 
ple does  not  absorb  all  the  oxygen.  If  the  temperature  is  too  high  this 
will  occur  and  no  oxygen  will  pass  through  the  apparatus. 

It  is  not  necessary  to  burn  all  the  metal  to  oxide;  the  time  that  would 
be  required  to  do  so  would  be  prohibitive  on  large  samples. 


CHAPTER  XX 

THE   DETERMINATION   OF   SPELTER   AND   TIN   PLATE 

COATING 

The  basis  of  this  test  is  as  follows : 

When  a  zinc-coated  iron  article  is  placed  in  lead  acetate  solution  at 
ordinary  temperatures,  the  zinc  passes  into  solution,  and  an  equivalent 
amount  of  metallic  lead  is  precipitated  in  a  loosely  adherent  form  upon 
the  specimen.  The  reaction  is  retarded  by  the  precipitation  of  the  lead, 
and,  therefore,  when  a  heavily  galvanized  piece  is  being  tested,  this  lead 
must  be  periodically  removed.  Should  lead  plate  on,  it  is  not  easily 
confounded  with  the  bright  iron  when  exposed.  The  uncovering  of  the 
iron  can  be  readily  detected. 

The  solution  used  for  making  this  test  is  prepared  by  dis- 
solving 400  grams  of  crystallized  lead  acetate  in  1  liter  of  water. 
When  'dissolved,  add  4  grams  of  finely  powdered  litharge,  and 
agitate  until  most  of  it  has  dissolved.  The  solution  is  allowed 
to  settle  and  the  clear  portion  decanted  for  use. 

Ordinary  glass  tumblers  have  been  found  very  satisfactory 
to  use  in  making  this  test,  as  they  are  the  right  diameter  to  enable 
the  sample  to  be  maintained  in  an  upright  position  without 
supports. 

The  samples  should  be  taken  from  various  parts  of  the  sheet. 
Use  several  2  in.  X  2  in.  pieces  cut  accurately.  Weigh  the 
samples  together  and  submerge  separately,  for  three  minutes,  in 
tumblers  containing  solution  of  lead  acetate.  The  samples  are 
then  taken  out  and  the  adherent  lead  removed  with  a  stiff  brush 
or  steel  spatula.  A  burnishing  action  should  be  avoided,  as 
under  some  conditions  closely  adherent  lead  will  be  plated  out  on 
the  iron.  Repeat  the  three-minute  immersions  in  the  lead  ace- 
tate solutions  until  a  bright  surface  is  exposed.  Four  three- 
minute  immersions  are  usually  sufficient.  Wash  specimens  in 
water,  dry  and  weigh.  The  loss  in  grams  represents  the  coating, 
which,  divided  by  the  number  of  2  in.  X2  in.  pieces  used  and 

189 


190  METALLURGICAL  ANALYSIS 

multiplied  by  1.27  gives  the  number  of  ounces  of  coating  per 
square  foot,  counting  the  zinc  as  from  one  side. 


ANALYSIS  OF  TIN  AND  TERNE  PLATE  AND  LEAD-COATED  SHEETS. 
METHOD  OF  THE  AMERICAN  ROLLING  MILLS  Co. 

Several  samples  exactly  2  in.  X  2  in.  should  be  taken  for 
analysis.  Clean  thoroughly  with  carbon  tetrachloride  or  gaso- 
line and  weigh.  A  400  c.c.  Jena  glass  beaker  has  been  found  the 
most  convenient  for  this  test.  We  have  found  that  20  c.c.  of 
concentrated  sulfuric  acid  is  sufficient  for  each  2  in.  X  2  in.  piece. 
If  four  pieces  are  taken,  however,  60  c.c.  of  sulfuric  acid  will  be 
sufficient.  Place  the  requisite  amount  of  acid  in  the  beaker  and 
heat  to  at  least  250°C.  Wrap  a  stiff  platinum  or  nickel  wire 
around  one  of  the  2  in.  X2  in.  pieces  so  that  it  can  be  placed  in 
the  acid  in  a  horizontal  position.  Immerse  the  piece  in  the  hot 
acid  for  exactly  one  minute.  Transfer  the  piece  to  another 
400  c.c.  beaker  containing  25  c.c.  of  distilled  water  and  rub  the 
surface  of  the  sample  while  washing  with  about  50  c.c.  more  dis- 
tilled water,  using  a  wash  bottle  for  this  purpose.  Dry  the  sam- 
ple thoroughly  and  reweigh.  The  loss  in  weight  represents  the 
coating  and  some  iron.  Repeat  this  operation  for  each  sample, 
collecting  all  rinsings  in  a  beaker,  and  reserve  for  analysis. 

The  iron  which  has  dissolved  is  determined  as  follows:  The 
sulfuric  acid  is  carefully  poured  into  the  beaker  containing  the 
washings  from  the  2  in.X2  in.  pieces.  This  solution  is  cooled 
and  poured  into  a  volumetric  flask.  Twenty-five  per  cent,  by 
volume  of  concentrated  hydrochloric  acid  is  added  and  the  flask 
filled  to  the  mark  with  distilled  water.  If  four  pieces  have  been 
taken  for  analysis,  a  500  c.c.  volumetric  flask  will  be  required. 
Use  a  proportionately  smaller  flask  if  less  than  four  samples  are 
analyzed.  Mix  thoroughly,  and  transfer  100  c.c.  of  the  solution 
to  a  300  c.c.  Erlenmeyer  flask.  Add  a  solution  of  tenth-normal 
permanganate  until  iron  and  tin  are  oxidized,  which  is  indicated 
by  the  appearance  of  a  permanent  straw  color.  No  account  is 
taken  of  the  amount  of  permanganate  used.  Heat  to  boiling 
and  reduce  carefully  with  stannous  chloride.  Cool  and  pour 
into  a  1000  c.c.  beaker  containing  500  c.c.  of  distilled  water  and 
25  c.c,  of  saturated  solution  of  mercuric  chloride,  stir  vigorously, 


SPELTER  AND  TIN  PLATE  COATING  191 

add  50  c.c.  of  the  titrating  mixture  of  phosphoric  acid  and  man- 
ganese sulfate,  and  titrate  with  tenth-normal  permanganate  to 
pink  color.  The  amount  of  iron  which  has  thus  been  determined 
is  subtracted  from  the  total  weight  lost  in  sulfuric  acid;  the  re- 
mainder is  coating.  It  is  very  often  unnecessary  to  make  an 
analysis  of  the  coating,  the  object  being  merely  to  determine  the 
weight. 

There  are  several  ways  of  expressing  the  weight  of  the  coating; 
we  prefer  to  express  it  in  ounces  per  square  foot.  By  knowing 
the  number  of  square  feet  in  a  box  of  tin  plate  or  a  case  of  terne 
plate  there  is  no  confusion  in  converting  the  ounces  per  square 
foot  to  pounds  per  box  or  case.  The  coating  on  tin  plate  is  some- 
times expressed  in  pounds  per  box  of  112  sheets  14  in.  X20  in. 
This  figure  can  be  obtained  by  multiplying  the  number  of  grams 
of  coating  of  each  2  in.  X2  in.  piece  by  17.29.  If  it  is  desired 
to  express  the  coating  on  terne  plate  in  pounds  per  case  of  112 
sheets  20  in.  X  28  in. ,  then  multiply  the  number  of  grams  of 
coating  on  each  2  in.  X2  in.  piece  by  34.57.  The  average  of 
the  several  pieces  represents  the  weight  of  coating. 

If  the  determination  of  tin  and  lead  is  desired  in  the  sheet, 
proceed  as  follows:  Place  another  100  c.c.  of  the  sulfuric  acid 
solution  containing  the  coating  in  a  300  c.c.  Erlenmeyer  flask. 
Whether  lead  sulfate  is  or  is  not  removed  with  this  100  c.c.,  does 
not  influence  the  accuracy  of  the  tin  analysis.  Add  50  c.c.  of 
concentrated  hydrochloric  acid  and  1  gram  of  finely  ground 
antimony.  Connect  flask  with  a  one-hole  stopper  containing  a 
glass  tube  bent  twice  at  right  angles,  the  end  of  which  projects 
into  a  beaker  of  water.  Boil  five  minutes  and  replace  the  beaker 
containing  the  water  with  one  containing  an  8  per  cent,  solution 
of  bicarbonate  of  soda  prepared  from  boiled  distilled  water. 
Remove  flask  from  hot  plate  and  allow  the  soda  water  to  flow 
back  into  the  flask  while  cooling  same  with  tap  water.  When 
cold,  add  a  few  cubic  centimeters  of  starch  solution  and  titrate 
to  permanent  blue  color  with  tenth-normal  iodine  solution.  One 
cubic  centimeter  equals  0.00595  gram  of  tin.  The  amount  of  tin 
found  is  subtracted  from  the  weight  of  coating  which  has  been 
determined  by  loss  in  sulfuric  acid,  and  after  the  iron  correction 
has  been  made  the  remainder  is  lead. 


192  METALLURGICAL  ANALYSIS 

An  example  of  a  regular  analysis  of  terne  plate  is  as  follows : 

Piece  2  in.  X2  in.  weight 7 . 563  grams 

Same  after  stripping  in  acid  weighs 6. 721  grams 


Loss,  coating  plus  iron  weighs 0.842  grams 

Sulfuric  acid  and  washings  were  diluted  to  200  c.c.,  100  c.c.  of  which 
was  titrated  for  iron.  This  required  10.1  c.c.  of  tenth-normal  perman- 
ganate, which  is  equivalent  to  0.0564  gram  of  iron.^  As  half  of  the 
solution  only  was  taken  for  analysis,  it  is  necessary  to  multiply  by  2, 
which  is  equivalent  to  0.1128  gram  iron. 

Total  weight  of  coating  plus  iron 0 . 8420  gram 

Weight  of  iron  dissolved 0 . 1 128  gram 


Coating 0. 7292  gram 

0.7292X34.57  =  25.21  Ib.  coating  per  case  of  112  sheets  20  in.  X28  in. 

The  tin  was  then  determined  in  50  c.c.  of  the  sulfuric  acid  solution. 
This  required  7.8  c.c.  of  tenth-normal  iodine. 

7.8X0.00595X4=0.1856  gram  tin 
Coating  Tin          Lead 

Grams  0.7292  =0.1856  =0.5436 

By  knowing  the  original  weight  of  coating  and  the  weight  of  tin  and 
lead  in  this  coating,  it  is  a  very  simple  matter  to  determine  the  percent- 
age of  each  element. 

In  the  determination  of  tin  in  tin  plate  it  is  only  necessary  to  determine 
the  loss  in  sulfuric  acid,  and  then  to  determine  the  iron  which  has  been 
dissolved,  the  remainder  being  tin. 

Heavily  coated  lead  sheets  may  require  twice  as  much  acid  and  a 
temperature  of  300°C,  to  completely  remove  the  coating  in  one  minute. 


CHAPTER  XXI 

THE  DETERMINATION  OF  ZINC  IN  ORES 

Zinc  usually  occurs  in  ores  as  sulfide,  oxide,  carbonate  or  hydro- 
silicate.  All  of  these  minerals  are  decomposed  by  boiling  in  the  proper 
mineral  acids.  Ores  containing  zinc  spinel  (Gahnite)  cannot  be  decom- 
posed by  acids  and  must  be  fused  before  treatment  with  acids.  Oxi- 
dized ores  should  be  first  treated  with  HC1  before  nitric  acid  is  used. 

Solutions  of  zinc  in  hydrochloric  acid  are  completely  precipitated  by 
potassium  ferrocyanide.  Many  other  metals  are  also  precipitated  by 
this  reagent  including  iron,  copper,  manganese,  and  cadmium,  and  if 
these  are  present  in  the  ore,  they  must  be  removed  before  the  zinc  is 
titrated. 

The  hydrochloric  acid  solution  of  zinc  which  is  to  be  titrated  must  not 
contain  free  chlorine,  bromine  or  oxides  of  chlorine,  as  these  decompose 
the  ferrocyanide  and  produce  a  green-colored  precipitate,  making  results 
run  high.  Zinc  ferrocyanide  is  white.  The  following  method  is  the 
process  of  von  Schulz  and  Low  modified.1 

Process  of  Analysis. — Place  1  gram  of  the  ore  in  a  250  c.c. 
beaker,  add  5  c.c.  of  concentrated  HC1,  heat  for  several  minutes, 
add  20  c.c.  of  HN03  and  boil  with  the  cover  on,  until  all  brown 
fumes  are  expelled.  Remove  the  beaker  from  the  heat,  add  1 
gram  of  KC1O3  and  boil  to  dryness.  A  blast  of  air  over  the  solu- 
tion greatly  expedites  the  evaporation.  Do  not  bake  the  residue. 
Now  add  50  c.c.  of  hot  water  and  J^  gram  of  KOH;  but  not  more 
than  this  amount  of  KOH.  Break  up  the  cake  on  the  bottom  of 
the  beaker  with  a  policeman,  then  add  7  grams  of  (NH^COa  and 
heat  nearly  to  boiling  for  several  minutes.  Let  the  precipitate 
settle,  filter,  preferably  by  suction,  and  wash  several  times  with 
a  hot  5  per  cent.  (NH4)2CO3  solution.  Wash  the  precipitate 
back  into  the  beaker  with  a  jet  of  water  from  the  wash  bottle. 
Dissolve  with  4  c.c.  of  HC1  and  a  little  KNQ2  to  reduce  the  MnO2 
which  may  be  present,  using  heat  to  hasten  the  solution.  Now 
add  strong  KOH  solution  until  all  free  acid  is  neutralized  and 

*Low,  "Technical  Methods  of  Ore  Analysis,"  DEMOREST,  J.  Am.  Chem. 
Soc.,  V,  302. 

13  193 


194  METALLURGICAL  ANALYSIS 

the  iron  precipitates,  but  do  not  add  an  excess  of  KOH.  Then 
add  5  grams  of  (NH4)2C03,  heat  to  boiling  and  filter  through  the 
same  paper  that  was  used  before.  Wash  several  times  with  hot 
ammonium  carbonate  solution. 

Make  the  filtrate,  which  should  amount  to  about  200  c.c.,  acid 
with  HC1,  keeping  the  cover  on  to  prevent  loss  due  to  efferves- 
cence. Then  add  20  c.c.  more  of  HC1,  sp.  gr.  1.2,  heat  to  70°, 
pass  H2S  through  the  solution  for  several  minutes,  and  when  the 
copper  is  practically  all  precipitated,  gradually  and  with  stirring 
add  10  c.c.  of  NH4OH,  sp.  gr.  0.9,  and  continue  to  pass  the  H2S 
for  several  minutes.  Again  heat  to  70°  and  titrate  with  ferro- 
cyanide.  The  volume  at  the  beginning  of  the  titration  should 
be  about  250  c.c.  Fifty  cubic  centimeters  of  this  may  be  re- 
served until  the  other  four-fifths  is  titrated,  then  the  50  c.c.  is 
added  and,  knowing  the  approximate  end  point,  the  titration  can 
be  finished  without  consuming  much  time.  The  titration  must 
be  performed  slowly  and  with  constant  stirring  to  get  the  best 
results. 

Standardization  of  the  Ferrocyanide. — Dissolve  22  grams  of 
pure  K4Fe(CN)6-3H2O  in  water  and  dilute  to  1  liter.  One  cubic 
centimeter  of  this  solution  will  precipitate  approximately  0.005 
gram  of  zinc. 

Weigh  0.2  gram  of  pure  zinc,  or  better,  the  amount  of  zinc 
which  is  approximately  that  which  the  sample  is  supposed  to 
contain.  Dissolve  in  10  c.c.  of  HC1  and  20  c.c.  of  H20,  add  10 
grams  of  NH4C1,  dilute  to  250  c.c.,  heat  to  70°  and  titrate.  Run 
in  the  ferrocyanide  slowly  and  with  constant  stirring  until  a  drop 
of  the  solution  shows  a  brown  tinge  when  tested  on  a  white  plate 
with  a  drop  of  a  5  per  cent,  solution  of  uranyl  nitrate  after  stand- 
ing a  minute. 

A  blank  must  be  run,  using  the  same  amount  of  reagents  and 
solution  as  in  the  standardization.  This  generally  takes  about 
0.3  c.c.  of  the  above  solution  and  this  amount  must  be  subtracted 
from  the  amount  of  ferrocyanide  used  in  the  standardization  and 
in  the  titration  of  the  ore.  It  is  necessary  that  standardization 
be  made  under  the  same  conditions  of  temperature,  volume,  and 
acidity  as  obtain  when  the  ore  is  titrated. 

Notes  on  the  Process. — Manganese  is  precipitated  at  the  first  from 
the  acid  solution  as  MnO2  by  means  of  potassium  chlorate  because  when 


THE  DETERMINATION  OF  ZINC  IN  ORES  195 

it  is  precipitated  from  an  alkaline  solution  as  Mn02  it  carries  down  zinc 
as  zinc  manganate. 

Potassium  hydroxide  is  used  to  combine  with  any  N03  ions  present  in 
order  to  prevent  the  formation  of  ammonium  nitrate  upon  the  addition 
of  ammonium  carbonate,  because  cadmium  carbonate  is  soluble  if  much 
ammonium  salt  other  than  the  carbonate  is  present. 

The  ammonium  carbonate  precipitates  the  lead,  cadmium  and  any 
manganese  in  solution  as  carbonates,  the  iron  and  aluminum  precipitate 
as  hydroxides  and,  of  course,  any  lime  or  magnesia  present  comes  down 
as  carbonate.  The  zinc  and  copper  dissolve  as  zinc  and  copper 
ammonia  carbonates.  If  the  amounts  of  the  elements  which  precipitate 
are  small  one  separation  is  enough  but  it  is  always  best  to  make  the 
double  separation  and  not  much  additional  time  is  consumed. 

When  the  copper  is  precipitated  according  to  the  above  directions, 
that  is,  by  hydrogen  sulfide  from  a  very  acid  solution,  the  copper  comes 
down  free  from  zinc.  What  little  copper  remains  in  solution  is  precipi- 
tated as  the  solution  is  gradually  made  less  acid.  The  copper  sulfide 
need  not  be  filtered  off,  as  it  does  not  interfere  with  the  titration  even 
when  the  copper  is  present  in  amounts  as  high  as  20  per  cent,  of  the  sam- 
ple, for  it  precipitates  in  a  very  dense  form. 

The  potassium  chlorate  used  in  the  decomposition  of  the  ore  intro- 
duces no  complications  unless  used  in  abnormally  large  amounts  for  it 
is  reduced  by  the  action  of  the  hydrogen  sulfide  and  the  presence  of  the 
hydrogen  sulfide  during  titration  prevents  any  oxidation  of  the  ferro- 
cyanide. 

The  use  of  lead  or  aluminium  to  precipitate  the  copper  and  cadmium  is 
inadvisable  as  they  tend  to  make  results  erratic.  Lead  is  least  harmful. 

The  titration  for  standardization  should  be  made  under  the  same  con- 
ditions as  to  temperature,  acidity,  volume,  amount  of  ammonium  salt, 
and  rate  of  titration  as  obtains  when  the  ore  is  titrated.  The  amount 
of  free  acid  should  not  be  greater  than  about  5  per  cent,  of  HC1,  sp.  gr. 
1.2. 

It  is  absolutely  necessary  that  the  titration  should  not  be  made  too 
rapidly.  If  the  ferrocyanide  be  run  in  rapidly  and  without  much  stir- 
ring, the  end  point  will  seem  to  be  reached  long  before  the  zinc  is  all  pre- 
cipitated. If,  however,  the  solution  be  then  allowed  to  stand  for  several 
minutes  while  being  vigorously  stirred,  the  titration  may  be  finished 
without  error.  Probably  when  the  ferrocyanide  is  added  rapidly,  zinc 
potassium  ferrocyanide  is  precipitated  which  can  react  with  uranyl 
nitrate  giving  a  brown  color. 

If  zinc  spinel  is  in  the  ore,  the  method  must  be  modified  as  follows: 
The  ore  is  dissolved  as  above.  The  gangue  left  on  the  filter  paper  should 


196  METALLURGICAL  ANALYSIS 

be  ignited  and  fused  with  the  sodium  carbonate  mixed  with  a  little 
borax  glass,  until  decomposition  is  complete.  The  melt  is  dissolved  in 
HC1  and  added  to  the  main  solution,  and  the  analysis  carried  on  as  usual. 
None  of  the  constituents  of  zinc  ores  interferes  with  the  above  process. 
Nickel  if  present  would  count  as  zinc.  The  writer  has  tested  the  method 
on  the  Government  standard  ore  which  contains  31.4  per  cent.  zinc. 
He  put  in  10  per  cent,  each  of  manganese,  iron,  copper,  lead  and  cadmium 
without  causing  more  than  Ho  to  Ko  Per  cent-  error- 
Method  of  Von  Schultz  and  Low. — Weigh  1  gram  into  a  4  in. 
casserole.  Add  2  or  3  c.c.  of  concentrated  HNOs,  then  cautiously 
25  c.c.  of  HNO3,  previously  saturated  with  KC1O3  by  shaking  up 
with  crystals  of  the  salt.  (Keep  this  solution  in  an  open  bottle.) 
When  the  violent  action  is  over,  cover  the  casserole  and  boil 
rapidly  to  dryness.  Do  not  bake  the  residue.  Now  cool  and 
add  7  grams  of  NH4C1,  25  c.c.  of  hot  water  and  15  c.c.  of  strong 
NH4OH.  Boil  the  liquid  one  minute,  add  bromine  water  and 
then  rub  the  dish  with  a  rubber-tipped  rod  to  loosen  and  disin- 
tegrate all  the  insoluble  matter.  Filter  and  wash  several  times 
with  a  boiling-hot  1  per  cent,  solution  of  NH4C1.  If  the  filtrate 
is  blue  copper  is  present. 

Add  to  the  filtrate  25  c.c.  of  concentrated  HC1  and  dilute  to 
200  c.c.  If  copper  is  present  add  40  grams  of  " granulated  lead" 
and  stir  until  the  liquid  is  colorless.  Titrate  the  hot  solution  as 
above  described. 

For  a  complete  bibliography  of  zinc  analysis  see  The  Journal 
of  Industrial  and  Engineering  Chemistry,  IV,  p.  468. 

The  Modified  Waring  Method  for  Zinc  (J.  Am.  Chem.  Soc.,  XXIX, 
265) . — This  method  is  accurate  and  especially  valuable  when  there  are 
large  amounts  of  manganese  present.  It  depends  upon  the  separation 
of  lead,  copper  and  cadmium  from  zinc  by  means  of  metallic  aluminium, 
and  zinc  from  iron,  aluminium  and  manganese  by  means  of  hydrogen 
sulfide  in  a  solution  very  slightly  acidified  with  formic  acid. 

Calamine,  willimite,  franklinite,  blende,  smithsonite  and  other  soluble 
minerals  are  decomposed  by  aqua  regia,  with  subsequent  evaporation 
with  sulfuric  acid  to  remove  nitrous  compounds.  If  zinc  spinel  (Gahn- 
ite)  is  present  the  insoluble  residue  must  be  fused  with  sodium  carbonate 
and  borax  glass,  the  fusion  dissolved  and  the  solution  added  to  the  main 
solution.  If  much  silica  is  present  the  borax  glass  may  be  dispensed  with. 
Silicates  such  as  cinders  from  oxide  furnaces  and  some  slags  and  natural 


THE  DETERMINATION  OF  ZINC  IN  ORES  197 

silicates  must  be  fused  with  sodium   carbonate  before  solution  with 
hydrochloric  acid. 

Process  of  Analysis  (For  soluble  ores). — Treat  0.5  gram  to 
1  gram  of  the  ore  in  an  Erlenmeyer  flask  with  10  c.c.  of  hydro- 
chloric acid  until  the  residue  is  white,  then  add  5  c.c.  of  nitric 
acid  and  5  c.c.  of  concentrated  sulfuric  acid  and  digest  until 
the  ore  is  completely  decomposed.  Then  evaporate  to  copious 
fumes  of  H2SO4  to  expel  all  nitric  and  hydrochloric  acids.  Dis- 
solve the  mass  in  50  c.c.  of  water  and  add  enough  sulfuric  acid 
to  bring  the  amount  of  free  acid  up  to  10  per  cent.  Introduce  a 
piece  of  sheet  aluminium  which  is  too  large  to  lie  flat  on  the  bot- 
tom of  the  beaker  and  boil  to  complete  reduction  (about  10 
minutes).  Filter  and  wash  through  a  filter  containing  pieces 
of  aluminium  to  keep  the  iron  reduced.  The  receiving  beaker 
should  contain  a  stirring  rod  of  aluminium.  Cool  the  solution, 
add  a  drop  of  methyl  orange,  and  neutralize  with  sodium  bi- 
carbonate to  a  light  straw  color.  Add  drop  by  drop  20  per 
cent,  formic  acid  until  the  pink  color  is  just  restored,  then  5 
drops  more.  (Dilute  hydrochloric,  1  :6,  may  be  substituted  for 
formic  acid  when  ammonium  thiocyanate  is  to  be  introduced.) 
Dilute  to  about  100  c.c.  for  each  0.1  gram  of  zinc  present;  if 
much  iron  is  present  add  2  to  4  grams  of  ammonium  thiocyanate, 
remove  the  strip  of  aluminium,  heat  nearly  to  boiling,  and  satu- 
rate with  hydrogen  sulfide.  Allow  the  pure  white  ZnS  to  settle 
a  few  minutes,  then  filter  and  wash  with  hot  water.  Transfer 
the  precipitate  and  filter  to  a  large  beaker,  dissolve  with  10  c.c. 
of  hydrochloric  acid  and  40  c.c.  of  water,  using  heat,  until  all 
zinc  is  in  solution.  Determine  the  zinc  as  pyrophosphate  con- 
taining 42.89  per  cent,  of  zinc,  or  by  titration  with  ferrocyanide. 

To  determine  the  zinc  as  pyrophosphate,  filter  the  solution  of 
the  ZnS  in  hydrochloric  acid  and  make  the  filtrate  cold,  dilute 
and  slightly  acid.  Then  add  a-  large  excess  of  ammonium 
sodium  hydrogen  phosphate  and  neutralize  very  carefully  with 
NH4OH,  adding  it  drop  by  drop,  finally  adding  a  drop  or  two 
in  excess.  Finally  add  about  1  c.c.  of  acetic  acid  and  warm 
gently  until  the  flocculent  precipitate  of  ZnNH4PO4.H2O  has 
settled  as  a  dense  crystalline  powder.  Filter  and  wash  with  hot 
water. 


198  METALLURGICAL  ANALYSIS 

Dry  the  precipitate,  separate  the  paper  from  it  and  burn  the 
paper.  Add  the  ash  to  the  precipitate  and  ignite  the  two, 
gently  at  first,  then  for  a  few  minutes  at  a  bright  red  heat.  Cool 
and  weigh  as  Zn2P2O7  containing  42.89  per  cent,  of  zinc. 

Instead  of  determining  the  zinc  gravimetrically  it  may  be 
finally  titrated  with  ferrocyanide  under  the  same  conditions  as 
previously  given. 

Notes  on  the  Process. — Any  copper  which  the  aluminium  does  not 
precipitate  will  come  down  with  the  zinc  but  will  not  dissolve  with  the 
latter  in  hydrochloric  acid. 

In  neutralizing,  if  the  solution  is  strongly  acid,  it  is  better  to  nearly 
neutralize  with  sodium  hydroxide  and  then  finish  with  bicarbonate. 
This  saves  time  and  prevents  loss  by  foaming. 

It  is  not  necessary  to  pass  the  hydrogen  sulfide  under  pressure  if  the 
diluting  is  done  as  directed.  The  gas  should  be  passed  through  until  a 
drop  of  the  solution  blackens  a  drop  of  alkaline  nickel  sulfate.  It  is 
necessary  that  the  solution  be  quite  hot  during  the  precipitation  of  the 
sulfide.  If  the  heating  has  taken  much  time  the.  formic  acid  may  have 
volatilized  and  more  must  be  added. 

The  flocculent  ZnNH4PO4.H20  is  very  soluble  in  the  mineral  acids  as 
well  as  in  ammonia,  but  after  crystallization  it  is  much  less  soluble  in 
the  latter.  It  is  only  slightly  soluble  in  acetic  acid;  an  excess  of  1  c.c. 
in  100  c.c.  of  solution  does  not  dissolve  an  appreciable  amount.  It  is 
somewhat  soluble  in  all  ammonium  salts  unless  considerable  excess  of 
phosphate  is  present. 


CHAPTER  XXII 

THE  DETERMINATION  OF  COPPER  IN  ORES 

Most  copper  ores  are  soluble  in  strong  mineral  acids.  In  dissolving  an 
ore  it  is  best  to  treat  first  with  hydrochloric  acid  to  dissolve  oxidized 
minerals,  then  with  nitric  acid  to  dissolve  sulfide  minerals.  Slags  may 
require  fusion  with  Na2C03  or  treatment  with  HF. 

There  are  in  general  use  four  methods  for  the  determination  of  cop- 
per in  ores.  They  are  the  iodide,  electrolytic,  cyanide  and  thiocyanate 
methods.  The  electrolytic  method  is  the  most  accurate  for  use  on  ores 
which  do  not  contain  arsenic,  antimony  or  bismuth,  but  for  analyzing 
these  impure  ores  or  miscellaneous  ores  whose  nature  is  not  known,  the 
iodide  method  is  the  most  applicable  because  it  is  accurate  and  rapid, 
and  the  above  elements  do  not  interfere. 

THE  IODIDE  METHOD  FOR  COPPER 

This  method  depends  upon  the  fact  that  in  a  solution  slightly  acid 
with  acetic  acid  cupric  compounds  oxidize  potassium  iodide  with  the  lib- 
eration of  iodine.  This  is  then  titrated  with  a  standard  thiosulfate 
solution.  The  reactions  are: 

Cu(N03)2+2KI  =  CuI+2KN03+I 
and,  2I+2Na2S2O3  =  2NaI+Na2S4O6. 

The  copper  iodide  is  precipitated  as  a  white  precipitate.  The  titra- 
tion  is  accurate  and  the  end  point  sharp.  Of  course  there  must  not  be 
anything  present,  besides  copper,  which  will  liberate  or  absorb  iodine. 
Nitrous  oxides,  ferric  ions,  free  bromine,  trivalent  arsenic  and  trivalent 
antimony  must  be  absent  as  they  will  either  absorb  or  liberate  iodine. 
Excess  of  free  mineral  acids  must  not  be  present.  Pentavalent  arsenic 
and  antimony  do  no  harm.  Bismuth  and  lead  if  present  in  solution 
cause  some  trouble  by  making  it  difficult  to  see  the  end  point  owing  to 
the  formation  of  yellow  iodides,  but  otherwise  cause  no  trouble.  The 
following  method  can  be  much  shortened  by  using  the  modification  on 
page  202. 

Process  for  Ores. — Take  enough  of  the  finely  ground  ore  for 
a,  sample  so  that  there  will  be  present  from  0.05  gram  to  0.40  gram 

199 


200  METALLURGICAL  ANALYSIS 

of  copper.  Put  in  a  250  c.c.  beaker  and  add  7  c.c.  of  concen- 
trated HC1  and  heat.  Then  add  10  c.c.  of  strong  HNO3  and 
heat  until  the  ore  is  completely  decomposed.  Then  add  7  c.c. 
of  strong  H2SO4  and  evaporate  until  the  sulfuric  acid  fumes 
strongly.  Cool  and  add  30  c.c.  of  water  and  heat  until  all 
soluble  salts  are  dissolved.  Cool,  add  4  grams  of  granulated 
zinc  and  shake  for  several  minutes.  The  copper  will  be  quickly 
precipitated.  Heat  until  the  zinc  is  dissolved,  then  add  25  c.c. 
of  H2S  water  to  make  sure  that  the  last  traces  of  copper  are 
precipitated.  Filter  and  wash  several  times  to  remove  all  iron 
salts.  Wash  the  precipitated  copper  back  into  the  beaker  with 
a  jet  of  water,  using  not  more  than  10  c.c.  of  water  if  possible, 
in  order  to  avoid  having  a  dilute  nitric  acid  solution.  Add 
7  c.c.  of  strong  HNO3,  heat  until  all  copper  goes  into  solution, 
and  boil  until  nitrous  fumes  are  expelled.  Then  pour  the  hot 
solution  through  the  filter  paper,  wash  the  paper  with  5  c.c. 
of  bromine  water  to  dissolve  any  copper  sulfide  there.  Finally 
wash  the  beaker  and  paper  thoroughly  with  water.  The  bro- 
mine also  oxidizes  any  nitrous  oxide  and  arsenic  or  antimony 
present. 

Heat  the  filtrate  to  boiling  and  boil  vigorously  for  not  less 
than  10  minutes  to  expel  all  bromine.  Cool  and  add  ammonia 
or  sodium  hydroxide  until  the  solution  turns  blue  or  becomes 
just  alkaline.  Do  not  add  an  excess  of  alkali.  If  an  excess  is 
added,  drop  in  a  few  drops  of  sulfuric  acid  until  the  excess  is 
neutralized,  then  add  alkali  again.  Now  add  acetic  acid  until 
the  liquid  becomes  acid,  then  add  2  or  3  c.c.  of  80  per  cent,  acetic 
acid  in  excess.  Cool  to  tap-water  temperature. 

Dissolve  3  grams  of  KI  in  a  few  cubic  centimeters  of  water,  add 
it  to  the  solution  to  be  titrated  and  stir  well.  It  immediately 
becomes  brown  due  to  the  liberated  iodine.  From  a  burette 
run  the  standard  thiosulfate  solution  in  until  the  brown  color  is 
nearly  gone,  then  add  5  c.c.  of  starch  solution.  Continue  the 
addition  of  the  thiosulfate  carefully  until  one  drop  turns  the  solu- 
tion from  a  blue  to  a  white  or  yellowish-white.  This  is  the  end 
point.  It  should  be  stable  and  the  blue  color  should  not  re- 
appear upon  standing  five  minutes.  If  the  blue  reappears  it 
indicates  faulty  work.  If  the  solution  is  not  sufficiently  acid 
the  end  will  not  be  sharp. 


THE  DETERMINATION  OF  COPPER  IN  ORES  201 

Standardization  of  the  Thiosulfate. — Dissolve  19.55  grams  of 
pure  Na2S2O3.5H20  in  water,  add  1  gram  of  NaOH  and  dilute 
to  1  liter.  The  water  should  be  free  from  CO2,  and  the  solution 
should  be  kept  in  the  dark.  Also  make  a  starch  solution  as 
directed  on  page  100. 

Weigh  carefully  about  0.2  gram  of  pure  copper  wire  or  foil. 
Place  in  a  250  c.c.  beaker  and  dissolve  in  10  c.c.  of  1 :1  HNOs. 
Dilute  to  25  c.c.,  boil  off  the  red  fumes,  then  add  5  c.c.  of  bromine 
water  and  boil  about  10  minutes  or  until  the  bromine  is  all  ex- 
pelled. Remove  from  the  heat,  dilute  to  75  c.c.,  add  NH4OH 
until  the  solution  becomes  just  alkaline  (becomes  blue)  but  not 
more.  Add  acetic  acid  until  the  solution  becomes  acid,  then  2 
c.c.  more  of  strong  acetic  acid.  Cool  to  tap- water  temperature, 
add  3  grams  of  KI  dissolved  in  15  c.c.  of  water  and  stir  a  moment. 
Now  run  in  the  thiosulfate  solution  from  a  burette  until  the 
yellow  color  of  free  iodine  has  nearly  gone  and  then  add  5  c.c. 
of  starch  solution.  This  should  produce  a  marked  blue  color. 
Continue  the  titration  cautiously  until  on  the  addition  of  another 
drop  the  blue  color  of  starch  iodide  disappears.  There  should 
be  no  difficulty  in  locating  the  end  point  within  a  single  drop. 
One  cubic  centimeter  of  the  thiosulfate  solution  should  be  equal 
to  0.005  gram  copper. 

Notes  on  the  Process. — Aluminium  may  be  used  in  place  of  zinc  to 
precipitate  the  copper  but  zinc  acts  more  rapidly  and  certainly.  It 
is  possible  to  precipitate  all  the  copper  with  the  zinc  but  is  best  to  add  the 
hydrogen  sulfide  always,  to  make  sure  of  complete  precipitation.  Of 
course  arsenic,  antimony,  silver,  bismuth,  etc.,  also  precipitate.  Lead 
remains  insoluble  as  lead  sulfate. 

The  addition  of  bromine  water  is  absolutely  necessary  in  analyzing 
ores  containing  arsenic  or  antimony  in  order  to  oxidize  them  to  the 
pentavalent  state.  If  they  are  not  so  oxidized,  the  iodine  liberated  by 
the  copper  will  be  used  up  in  oxidizing  arsenic  and  antimony  from  triva- 
lent  to  pentavalent  condition.  The  bromine  also  insures  complete  solu- 
tion of  the  copper  sulfide  and  absence  of  nitrous  oxides.  Excess  bromine 
must,  of  course,  be  boiled  off. 

It  is  necessary  to  use  a  large  excess  of  KI  to  hold  the  liberated  iodine 
in  solution  and  make  the  reaction  rapid. 

Lead  and  bismuth  having  yellow  iodides  cause  trouble  if  present  by 
making  it  very  difficult  to  tell  when  to  add  the  starch,  but  with  experi- 
ence this  is  not  a  serious  trouble.  No  other  elements  cause  trouble. 


202  METALLURGICAL  ANALYSIS 

It  is  necessary  that  the  acetic  acid  be  added  to  a  solution  not  too  alka- 
line, as  the  acetate  formed  on  adding  the  acid  to  an  alkaline  solution 
decreases  the  ionization  of  the  acetic  acid  (according  to  a  well-known 
law)  thus  making  the  solution  insufficiently  acid  for  the  reaction  between 
the  copper  and  the  iodide  to  be  complete,  causing  an  indefinite  end  point. 

If  the  end  point  is  overrun,  simply  add  1  c.c.  of  a  copper  sulfate  solu- 
tion containing  0.01  gram  of  copper  per  cubic  centimeter,  then  complete 
the  titration  and  subtract  0.01  gram  from  the  total  amount  of  copper 
found. 

When  the  ore  contains  arsenic  or  antimony,  it  is  necessary  to  use 
bromine  after  the  solution  of  the  ore  has  been  evaporated  to  sulfuric 
acid  fumes,  for  even  if  the  ore  is  dissolved  in  aqua  regia,  after  evaporation 
to  fumes  of  sulfuric  acid  the  arsenic  and  antimony  are  present  as  the 
trivalent  elements. 

SHORT  IODIDE  METHOD  FOR  COPPER 

The  following  process  is  a  modification  of  the  process  of  Mott.1 
The  process  is  very  rapid  and  according  to  the  writer's  experience  the 
results  obtained  by  its  use  are  nearly  as  good  as  by  the  long  iodide 
method. 

The  copper  is  not  separated  from  the  other  metals.  This  makes  it 
necessary  to  remove  any  ferric  ions  which,  if  present,  would  liberate 
iodine  and  cause  results  to  be  high.  These  ferric  ions  are  removed  by 
adding  ammonium  fluoride  which  forms  with  the  iron  undissociated 
ferric  fluoride,  which,  since  it  is  undissociated,  has  no  oxidizing  power 
and  cannot  liberate  iodine  under  the  conditions  of  the  solution. 

Process  of  Analysis. — Dissolve  a  sufficient  sample  of  the  ore 
in  5  c.c.  of  strong  HC1  and  7  c.c.  of  HN03,  heating  the  solution 
to  boiling.  When  action  has  ceased,  add  10  c.c.  of  1:1  H2SO4 
and  evaporate  rapidly  until  the  sulfuric  acid  fumes  strongly. 
Cool  and  add  30  c.c.  of  water,  heat  until  all  soluble  salts  are  in 
solution,  then  add  5  c.c.  of  bromine  water  and  boil  vigorously  for 
10  minutes  or  until  all  bromine  has  gone.  Now  add  NH4OH 
until  ferric  hydroxide  persists  on  shaking,  then  add  2  or  3  c.c. 
of  80  per  cent,  acetic  acid,  cool  to  tap-water  temperature,  add 
2  grams  of  HN4F  and  stir  until  it  is  dissolved.  The  ferric  hy- 
droxide will  immediately  dissolve  but  the  solution  will  be  turbid. 
Add  2  grams  of  KI  dissolved  in  water  and  titrate  as  usual. 

1  The  Chemist-Analyst,  July,  1912. 


THE  DETERMINATION  OF  COPPER  IN  ORES  203 

Notes  on  the  Process. — The  thiosulfate  should  be  standardized  by 
dissolving  0.20  gram  of  copper  and  about  0.10  gram  of  iron  in  nitric  acid 
and  treating  the  solution  exactly  like  an  ore  solution. 

After  the  titration  is  finished  the  solution  should  be  emptied  out  of  the 
beaker,  as  the  beaker  will  be  etched  by  the  HF  on  long  standing. 

The  writer  has  used  this  method  on  samples  containing  10  per  cent, 
of  iron,  5  per  cent,  arsenic,  and  7  per  cent,  antimony  with  perfect 
results  when  compared  with  the  long  iodide  method. 

The  writer  often  combines  the  sulfocyanate  precipitation  with 
the  thiosulfate  titration. 

REFERENCES  FOR  THE  IODIDE  METHOD: 

PETERS,  J.  Am.  Chem.  Soc.,  XXXIV,  p.  422.     Sources  of  error  in 

standardization. 

VIDEGREN,  Z.  anal  Chem.,  XLVIII,  539. 
McCLURE,  Mining  Sci.  Press,  CIII,  48. 
LATHE,  Eng.  Mining  J.,  XCIII,  1073.     Methods  used  at  Granby. 

THE  ELECTROLYTIC  DETERMINATION  OF  COPPER  IN  ORES,  ETC. 

The  electrolytic  precipitation  of  copper  is  the  most  accurate  method 
of  determining  of  copper  when  the  conditions  are  right.  Ores  con- 
taining arsenic,  antimony,  bismuth,  or  selenium  or  tellurium  are  perhaps 
not  best  analyzed  by  the  electrolytic  method.  It  is  true  that  the  elec- 
trolytic separation  of  copper  from  these  elements  can  be  made  but  the 
methods  are  not  usable  technically.  So  if  these  interfering  elements  are 
present  they  must  be  separated  by  purely  chemical  methods  before  the 
copper  is  electrolyzed.  Methods  involving  delicate  adjustment  of 
potential  for  the  separation  of  elements,  while  interesting  from  a 
scientific  standpoint,  are  too  troublesome  to  be  used  in  technical  analy- 
sis; the  only  electrolytic  methods  used  are  those  in  which  separation 
depends  upon  choice  of  electrolyte;  some  elements  will  separate  from 
acid  solutions,  some  will  not.  Some  will  separate  from  sulfide  solu- 
tions, some  will  not.  Thus  copper  can  be  separated  electrolytically 
from  iron,  aluminium,  zinc,  etc.,  from  a  dilute  nitric  or  sulfuric  acid 
solution. 

The  deposition  of  copper  should  take  place  from  a  solution  free  from 
hydrochloric  acid  (except  under  special  conditions),  free  from  interfering 
elements,  and  not  too  acid  with  either  nitric  or  sulfuric  acids.  It  is 
important  that  the  current  density  at  the  cathode  be  not  too  great. 
The  current  density  depends  upon  the  size  of  the  cathode,  the  distance 
between  the  electrodes,  the  conductivity  of  the  solution  and  the  drop 
of  potential  between  the  electrodes.  If  the  current  density  be  too 
great  the  copper  will  deposit  in  a  non-adherent  condition. 


204  METALLURGICAL  ANALYSIS 

If  the  solution  is  kept  vigorously  stirred  so  that  the  copper  ions  are 
kept  coming  in  contact  with  the  cathode  rapidly,  the  precipitation  of 
the  copper  is  more  rapid  and  the  current  density  employed  may  be  much 
greater  without  getting  a  poor  deposit.  If  a  gauze  cathode  is  used  an 
enormously  greater  current  density  may  be  used  than  if  a  plain  cathode  be 
used.  A  plain  flat  cathode  should  be  sand  blasted  or  roughened  in 
some  way  so  that  the  copper  deposit  will  be  more  adherent. 

Method  for  Ores  free  from  Arsenic,  Antimony  and  Bismuth. — 
Use  for  a  sample  an  amount  of  ore  which  will  contain  not  more 
than  0.20  gram  of  copper.  The  sample  must  be  finely  ground. 
Put  in  a  150  c.c.  beaker  and  add  15  c.c.  of  a  mixture  of  equal  parts 
of  HNO3  and  HC1.  Heat  until  decomposition  of  the  ore  is  com- 
plete. Add  4  c.c.  of  H2SO4  and  evaporate  to  copious  fumes  of 
S03.  Cool,  add  25  c.c.  of  water  and  5  c.c.  of  HN03  and  heat 
until  all  soluble  salts  are  dissolved.  Dilute  to  125  c.c.  and  filter 
if  the  residue  is  such  as  not  to  settle  clear.  If  it  settles  well  it  is 
not  necessary  to  filter.  The  solution  is  now  ready  for  electroly- 
sis. If  silver  is  present  add  just  enough  NaCl  solution  to  pre- 
cipitate it. 

The  details  of  the  electrolysis  will  depend  upon  the  nature  of 
the  cathode.  If  a  plain  electrode  is  to  be  used  add  1  c.c.  of  the 
"nitro  preparation,"1  if  a  gauze  electrode  is  used  it  is  not  needed. 
Connect  to  a  suitable  source  of  electric  potential  and  adjust  the 
rheostat  until  the  proper  current  density  on  the  cathode  is  at- 
tained. If  a  plain  cathode  is  used  the  current  density  should  be 
from  0.1  ampere  to  0.5  ampere  per  100  sq.  cm.  of  surface,  depend- 
ing upon  the  roughness  of  the  surface  and  amount  of  copper  to 
be  deposited.  The  rougher  the  surface  and  the  less  the  copper 
present  the  greater  the  current  density  that  may  be  employed. 
With  a  plain  electrode  the  time  required  will  be  from  four  hours 
to  over  night  unless  the  solution  be  continually  stirred.  If  the 
solution  be  kept  agitated  the  time  required  may  be  greatly  re- 
duced. If  a  gauze  cathode  be  used  the  electrolysis  may  be  com- 
pleted in  from  15  minutes  to  an  hour  with  a  current  of  5  amperes 
without  the  trouble  incident  to  a  mechanical  stirrer  or  solenoid 
and  still  beautiful  and  adherent  deposits  of  copper  are  obtained. 

1  The  "Nitro  Preparation"  is  made  by  G.  A.  Guess  as  follows:  Warm 
10  grams  of  No.  4  hard  oil  or  vaseline  with  100  c.c.  of  strong  HNO3  until  the 
action  ceases,  then  dilute  to  300  c.c.  and  filter. 


THE  DETERMINATION  OF  COPPER  IN  ORES  205 

The  writer  uses  gauze  cathodes  and  has  abandoned  mechanical 
stirring  of  the  solution  as  being  unnecessary  and  troublesome. 
If  stirring  of  the  solution  be  done,  it  is  best  to  use  a  rotating 
magnetic  field  produced  by  a  solenoid. 

Continue  the  passage  of  the  current  until  the  copper  seems  all 
precipitated,  then  withdraw  J^  c.c.  with  a  pipette  and  add  it  to 
a  similar  amount  of  H2S  water  on  a  paraffined  white  plate.  (The 
liquid  will  not  run  on  the  paraffined  plate.)  If  the  slightest 
amount  of  copper  remains  the  test  will  darken.  If  the  test  shows 
that  the  copper  is  all  precipitated,  lift  the  cathode  quickly  out 
of  the  solution  and  set  in  a  beaker  of  distilled  water.  Then  wash 
it  with  alcohol,  dry  on  a  steam  plate  or  in  an  oven  at  about  100°, 
cool  and  weigh.  The  copper  should  be  crystalline  and  beauti- 
fully bright  and  too  firm  to  be  scratched  off  with  the  finger-nail. 
If  it  is  firm  but  dull  in  color  it  indicates  the  presence  of  one  of  the 
interfering  elements.  The  precipitate  should  not  be  dried  by 
moistening  it  with  alcohol  and  setting  fire  to  the  alcohol  as  this 
causes  some  oxidation  of  the  copper.  The  weight  of  the  cathode 
and  copper  minus  the  weight  of  the  cathode  divided  by  the 
weight  of  the  sample,  then  multiplied  by  100  gives  the  percentage 
of  copper  in  the  sample. 

REFERENCES: 

See  SPILLSBURY,  Eng.  Mining  J.,  LXXXIV,  773.  Short  method 
using  "nitro." 

GUESS,  Eng.  Mining  «/.,  1906,  328.  Electrolytic  assay  for  Pb  and 
Cu. 

HEATH,  «/.  Ind.  Eng.  Chem.,  Ill,  73.  Exact  electrolytic  assay  of 
copper. 

TRAPHAGEN,  Chem.  News,  CIV,  69. 

CAVEN  and  CHAD  WICK,  Eng.  Mining  J.,  LXXXIX,  954.  Electro- 
lytic methods  for  slags,  ores,  mattes,  and  blister  copper. 

BENNER,  J.  Ind.  Eng.  Chem.,  II,  195,  and  Met.  Chem.  Eng.,  IX,  141. 
Use  of  gauze  cathode  in  technical  analysis. 

The  source  of  the  electric  current  may  be  a  direct  current  power  line 
or  storage  batteries  or  primary  cells  or  an  alternating  current  power  line. 
If  a  direct  current  power  line  is  used  all  that  is  necessary  is  a  proper 
rheostat  and  ammeter  in  series  with  the  electrolysis  cell.  If  direct 
current  line  is  not  available  but  an  alternating  current  is,  it  may  be  used 
in  connection  with  a  chemical  rectifier  or  a  motor  generator  set.  Storage 
batteries  are  very  convenient,  especially  when  only  alternating  current 


206 


METALLURGICAL  ANALYSIS 


power  is  available  and  it  is  not  desired  to  keep  a  rectifier  running  con- 
tinuously. The  writer  uses  a  chemical  rectifier  in  connection  with 
alternating  current  to  charge  storage  battery  from  which  current  for 
electrolysis  is  obtained.  The  rectifier  cost  about  $10  to  build  and  has 
been  in  service  for  several  years  with  perfectly  satisfactory  results. 
It  is  shown  in  Fig.  13. 

A-A-A-A  are  aluminium  plates  10X4  in.  in  size.  L-L-L-L  are 
lead  plates  of  the  same  size.  These  plates  are  attached  to  brass  rods 
which  pass  through  a  hard  rubber  board,  and  are  fastened  by  nuts  to 

the  bars  B,  C,  D  and  E.  To  bar  B 
are  attached  two  aluminium  plates, 
to  bar  C  are  attached  a  lead  and 
an  aluminium  plate,  to  bar  D  are 
attached  two  lead  plates,  and  to  bar 
E  are  attached  a  lead  and  an  alumi- 
nium plate.  The  alternating  termi- 
nals are  on  the  bars  C  and  E.  The 
direct  current  terminals  are  on  the 
bars  B  and  D.  The  plates  hang  in 
the  jars  J-J-J-J,  which  are  filled  with 
a  saturated  ammonium  phosphate 
solution.  The  jars  set  in  a  tank 
of  water  to  keep  them  cool.  The 
alternating  current  impulses  can- 
not pass  through  the  solution  from 
aluminium  plates  to  lead  plates,  but 
can  pass  from  lead  plates  to  alumi- 
nium plates.  Thus  both  of  the  alter- 
nating current  impulses  are  sent  in 
the  same  direction  out  from  bar  B, 
to  do  whatever  work  is  desired,  and 

returned  through  bar  D.  The  alternating  potential  between  C  and  E 
must  not  be  greater  than  25  volts. 

Method  for  Impure  Ores. — Ores  containing  arsenic,  antimony,  or 
bismuth  cannot  be  electrolyzed  for  copper  without  first  separating  the 
copper  from  these  elements  by  purely  chemical  means.  The  following 
method  makes  the  separation  by  one  filtration  and  gives  accurate  results. 
It  depends  upon  the  fact  that  cuprous  copper  may  be  precipitated  com- 
pletely and  free  from  the  above  elements  by  means  of  potassium  thio- 
cyanate  (KCNS)  from  a  solution  slightly  acid  and  containing  tartaric 
acid.  The  CuCNS  is  dissolved  and  electrolyzed  after  the  thiocyanic 
acid  is  destroyed. 


FIG.  13. 


THE  DETERMINATION  OF  COPPER  IN  ORES  207 

Process  of  Analysis. — Dissolve  a  sufficient  weight  of  the  sam- 
ple in  7  c.c.  of  HC1  and  7  c.c.  of  HNOs.  When  the  ore  is  decom- 
posed add  5  c.c.  of  H2S04  and  evaporate  to  fumes  of  H2SO4. 
Cool  and  add  25  c.c.  of  water  in  which  is  dissolved  3  grams  of  tar- 
taric  acid  and  heat  until  all  soluble  salts  are  in  solution.  Filter 
and  wash  the  residue  well  with  water.  Add  NH4OH  until  the 
solution  becomes  alkaline,  then  add  H2SO4  until  the  solution  is 
acid,  then  1  c.c.  in  excess.  This  makes  the  solution  slightly  acid 
with  tartaric  acid.  Now  add  2  grams  of  Na2SO3  to  reduce  the 
copper  to  the  monovalent  ion,  heat  nearly  to  boiling  and  add  1 
gram  of  KCNS  dissolved  in  water.  The  CuCNS  precipitates 
immediately  as  a  dense  white  precipitate  but  the  solution  will  be 
colored  red  if  there  be  trivalent  iron  present.  This  does  no  harm. 
Stir  well  and  allow  the  CuCNS  to  settle  for  several  minutes 
Then  filter  through  a  close  filter  and  wash  five  times  with  a  warm 
solution  containing  a  little  KCNS  and  tartaric  acid. 

Poke  a  hole  through  the  paper  and  wash  the  precipitate  through 
with  a  little  water.  Now  pour  through  the  filter  15  c.c.  of  a  1 :  2 
HNO3  solution.  When  the  acid  has  run  through,  wash  well 
with  water  but  keep  the  volume  of  the  filtrate  down  to  at  least 
50  c.c.  Now  boil  vigorously  for  5  to  10  minutes  to  destroy  the 
HCNS,  cool,  dilute  to  125  c.c.  and  electrolyze,  using  a  gauze 
cathode  and  a  large  current.  The  writer  uses  a  gauze  cathode 
of  cylindrical  form  1  in.  in  diameter  and  2.5  in.  high  and  a  cur- 
rent of  2  amperes  for  10  minutes,  then  a  current  of  4  amperes 
until  the  precipitation  is  complete  as  shown  by  a  test  on  a  white 
plate  wiih  H2S.  Precipitation  is  complete  in  one-half  hour  to 
an  hour.  Set  the  cathode  quickly  into  a  beaker  of  distilled  water, 
then  wash  with  alcohol,  dry  at  100°  and  weigh. 

Notes  on  the  Process.— The  tartaric  acid  is  added  to  keep  antimony 
in  solution  and  because  the  presence  of  tartaric  acid  is  desired  when  the 
copper  is  precipitated.  If  the  ore  contains  lead,  the  sulfate  formed 
goes  into  solution  when  the  tartaric  acid  is  neutralized  if  it  is  not  filtered 
off. 

If  the  lead  is  in  solution  some  of  it  precipitates  when  the  sulfite  is 
added  and  is  left  oh  the  paper  when  the  CuCNS  is  dissolved,  but  this 
does  no  harm  as  it  precipitates  on  the  anode  during  electrolysis,  nor 
does  the  presence  of  large  amounts  of  ferric  iron.  The  writer  has  pre- 
cipitated 0.2  gram  of  copper  from  0.2  gram  of  iron,  0.1  gram  of  arsenic, 


208  METALLURGICAL  ANALYSIS 

0.1  gram  of  antimony  and  0.1  gram  of  bismuth  and  large  amounts  of  lead 
and  always  obtained  excellent  results,  correct  almost  to  the  limit  of  error 
of  weighing  on  an  ordinary  analytical  balance. 

It  is  necessary  to  destroy  the  HCNS  because  the  copper  precipitates 
by  electrolysis  in  a  very  spongy  condition  if  there  is  HCNS  in  solution. 

Instead  of  dissolving  the  CuCN$  in  acid  and  destroying  the  HCNS 
by  boiling,  the  CuCNS  on  the  paper  may  be  ignited  in  a  porcelain 
crucible  until  the  paper  is  all  burnt  off  and  then  the  CuO  formed  dis- 
solved in  5  c.c.  of  HNO3,  the  solution  diluted  to  125  c.c.  and  electrolyzed. 

Under  the  conditions  given  above  one  fully  charged  lead  storage  cell 
without  a  rheostat  in  series  will  give  a  drop  of  potential  between  the 
electrodes  of  2  volts  and  a  current  of  %  ampere.  Two  cells  will  give 
a  drop  between  the  electrodes  of  about  3  volts  and  a  current  of  3  amperes 
and  three  cells  of  10  amperes  capacity  a  drop  of  3.5  volts  and  5.5  am- 
peres. So  that  when  a  gauze  cathode  is  used  a  rheostat  is  not  necessary 
to  reduce  the  current. 

REFERENCE: 

DEMOREST,  J.  Ind.  Eng.  Chem.,  V,  216. 

The  Guess-Haultain  electrolytic  cabinets  are  made  so  that  200  or 
more  determinations  may  be  made  in  a  day. 

For  the  methods  of  electrolytic  separation  of  copper  from  arsenic, 
antimony,  bismuth,  silver,  mercury  and  other  elements,  see  "  Electro- 
analysis"  by  E.  F.  SMITH  and  " Practical  Methods  of  Electro-chemistry" 
by  F.  M.  PERKIN. 


THE  CYANIDE  METHOD  FOR  COPPER  IN  ORES 

When  a  nitric  acid  solution  of  copper  is  made  alkaline  with  ammonia 
it  becomes  intensely  blue  owing  to  the  formation  of  the  compound 
Cu(NH3)4(N03)2.  When  a  solution  of  KCN  is  added  to  this  blue  solu- 
tion it  becomes  less  and  less  blue  and  finally  colorless  owing  to  the  for- 
mation of  colorless  K5NH4Cu2(CN)8,1  the  copper  thus  changing  from 
a  part  of  a  colored  cation  to  a  part  of  a  colorless  anion  in  which  it  is 
univalent. 

The  amount  of  KCN  required  to  titrate  a  copper  solution  depends 
upon  the  temperature  of  the  solution,  the  volume,  the  amount  of  am- 
monium salts  and  the  amount  of  free  ammonia  present.  Therefore  to 
get  good  results  these  conditions  must  be  the  same  when  the  copper  from 

1  "Analytical  Chemistry,"  TREADWELL-HALL,  Vol.  I,  p.  172. 


THE  DETERMINATION  OF  COPPER  IN  ORES  209 

the  sample  is  titrated  as  when  the  KCN  is  standardized.     This  is 
absolutely  necessary. 

Any  nickel,  silver  or  zinc  present  will  also  be  titrated  with  the  KCN 
and  so  must  be  removed. 

Process  of  Analysis. — Dissolve  1  gram  of  ore  with  5  c.c.  of 
HC1  and  5  c.c.  of  HNO3.  Add  7  c.c.  of  H2SO4  and  evaporate 
until  the  H2SO4  fumes  copiously.  Cool,  add  30  c.c.  of  water  and 
heat  until  all  ferric  salts  are  dissolved.  Again  cool  and  add  4 
grams  of  pure  granulated  zinc  and  shake  for  five  minutes.  Heat 
until  the  zinc  is  all  dissolved,  then  add  25  c.c.  of  H2S  water. 
Filter  through  a  funnel,  into  the  apex  of  which  is  stuffed  a  plug 
(made  by  shaking  a  mixture  of  equal  amounts  of  glass  wool  and 
asbestos  and  then  pouring  in  the  funnel).  Wash  the  precipi- 
tated copper  until  all  zinc  salts  are  removed,  wash  the  copper  back 
into  the  flask,  place  the  flask  under  the  funnel  and  pour  through 
10  c.c.  of  a  hot  1 : 1  HNO3  solution.  Pour  the  same  solution 
through  several  times,  if  necessary,  to  get  all  the  copper  dissolved. 
Finally  wash  well  to  remove  all  the  copper  nitrate.  Do  not  use 
more  than  10  c.c.  of  HN03,  sp.  gr.  1.10,  in  dissolving  the  copper. 

Now  boil  to  remove  red  fumes,  dilute  to  125  c.c.  and  if  silver  is 
present  add  a  drop  of  HC1  and  filter  off  the  AgCl.  Add  10  c.c.  of 
NH4OH,  sp.  gr.  0.9,  cool  to  room  temperature  and  titrate. 

Run  in  the  standard  cyanide  solution  slowly  and  with  constant 
shaking  until  the  blue  color  is  almost  gone. 

The  solution  will  now  generally  be  turbid.  Filter,  wash  once, 
dilute  to  180  c.c.,  and  carefully  complete  the  titration  by  adding 
the  cyanide  drop  by  drop,  shaking  the  solution  after  each  drop 
until  the  blue  tinge  just  disappears. 

Standard  Cyanide  Solution. — Dissolve  21  grams  of  pure  KCN 
and  2  grams  of  KOH  in  distilled  water,  dilute  to  1  liter,  and  mix 
well.  One  cubic  centimeter  is  equal  to  about  0.005  gram  of 
copper.  Now  weigh  accurately  0.2  gram  of  pure  copper  wire  or 
foil  and  dissolve  in  a  250  c.c.  Erlenmeyer  flask  with  10  c.c.  of 
1:1  HNO3.  Boil  off  the  red  fumes  and  dilute  to  125  c.c.  Add 
10  c.c.  of  NH4OH,  cool  to  room  temperature,  and  titrate  with  the 
KCN  solution  slowly  until  the  blue  is  nearly  gone.  Now  dilute 
to  180  c.c.  and  carefully  finish  the  titration  until  the  blue  just 
disappears. 

14 


210  METALLURGICAL  ANALYSIS 

Notes  on  the  Process.  —  The  zinc  used  to  precipitate  the  copper  must 
be  all  dissolved.  This  can  be  told  by  the  cessation  of  the  effervescence. 
If  the  solution  becomes  too  concentrated,  ZnS04  separates  out  and  stops 
the  solution. 

If  the  H2S  causes  a  precipitation  of  copper  sulfide,  the  filter  should  be 
washed  with  5  c.c.  of  bromine  water  after  the  copper  has  been  dissolved 
with  HNO3.  This  dissolves  the  sulfide. 

If  the  titration  is  made  rapidly  the  blue  color  will  persist  even  after 
enough  HCN  has  been  added  to  react  with  all  the  copper.  This  is 
because  the  reaction  takes  some  time  for  completion.  Hence  the  titra- 
tion must  be  made  slowly. 

A  concentrated  solution  requires  more  cyanide  for  decoloration  than  a 
dilute  one.  A  hot  solution  requires  less  than  a  cold  one.  The  amount 
of  cyanide  required  is  affected  by  the  amount  of  ammonia  or  ammonium 
salts  present.  Hence  the  condition  should  be  the  same  when  the  ore  is 
titrated  as  when  the  cyanide  is  standardized. 

The  KCN  solution  keeps  better  when  the  KOH  is  added. 

If  only  an  approximate  determination  of  the  copper  is  desired,  it  can 
be  made  very  rapidly  by  omitting  the  zinc  precipitation.  In  this  case 
treat  1  gram  of  the  ore  with  5  c.c.  concentrated  HN03,  and  boil  till  the 
copper  is  extracted  and  most  of  the  acid  driven  off.  Now  add  5  c.c. 
more  HNO3,  dilute  to  125  c.c.,  add  10  c.c.  of  strong  NH4OH  and  run 
in  the  cyanide  till  the  blue  color  is  nearly  discharged.  Filter  off  and 
finish  the  titration  as  before.  If  there  is  a  very  large  precipitate  of 
Fe(OH)3,  repeat  the  process  on  a  new  sample  of  ore,  adding  nearly 
sufficient  cyanide  solutions  as  calculated  from  the  first  determination 
before  filtering. 

SULFOCYANATE-PERMANGANATE  METHOD  FOR  COPPER 

As  said  on  page  206,  copper  can  be  completely  precipitated  as  CuCNS. 
When  this  precipitate  is  acted  upon  by  a  caustic  alkali  the  following 
reaction  takes  place:  CuCNS+NaOH  =  CuOH+NaCNS.  The  CuOH 
is  left  on  the  filter  while  the  NaCNS  goes  into  solution.  The  sulfo- 
cyanic  acid  is  titrated  by  a  standard  solution  of  permanganate,  the  final 
results  of  the  oxidation  being  expressed  thus: 


That  is,  the  sulfocyanic  acid  equivalent  to  1  atom  of  copper  requires 
3  atoms  of  oxygen  to  oxidize  it,  which  is  the  amount  of  oxygen  required 
to  oxidize  6  atoms  of  iron  from  divalent  to  trivalent  condition.  Then  to 
get  the  copper  value  of  the  permanganate  from  the  iron  value  we  make 


THE  DETERMINATION  OF  COPPER  IN  ORES  211 

the  following  proportion,  Cu  :6Fe  :63.57  : 335.04,  or  the  iron  value  mul- 
tiplied by  0.1897  gives  the  copper  value  of  the  permanganate. 

When  this  titration  is  performed  in  acid  solution  the  reaction  is  not 
strictly  in  accord  with  the  above  written  one  and  an  empirical  factor 
must  be  used,  raising  the  calculated  value  for  the  permanganate  by  about 
5  per  cent.  When  the  titration  is  made  in  an  alkaline  solution,  as 
described  below,  the  titration  takes  place  in  accord  with  the  above 
reaction  and  the  iron  value  of  the  permanganate  used  multiplied  by 
0.1897  gives  the  amount  of  copper  present.  No  elements  interfere. 

Process  of  Analysis. — Place  1  gram  or  a  sufficient  amount 
of  the  ore  (or  metal)  in  a  200  c.c.  beaker,  add  5  c.c.  of  HC1  and 
heat  a  few  minutes,  then  add  10  c.c.  of  HNO3  and  heat  until 
the  ore  is  decomposed.  Then  add  10  c.c.  of  1 :1  H2SO4  and  evapo- 
rate to  fumes  of  SO3.  Add  50  c.c.  of  water  containing  3  grams  of 
tartaric  acid  and  heat  until  all  soluble  salts  are  dissolved.  Filter 
and  wash,  cool  and  add  NH4OH  until  the  solution  becomes  alka- 
line (or  becomes  deep  blue).  Then  add  H2SO4  until  the  liquid  is 
acid,  and  then  lj^  c.c.  more  of  strong  acid,  sp.  gr.  1.84.  Heat 
nearly  to  boiling  and  add  1  gram  of  Na2SOs  dissolved  in  water 
and  then  pour  in  slowly  and  with  vigorous  stirring  1  gram  of 
KCNS  dissolved  in  20  c.c.  of  water.  Allow  the  beaker  to  remain 
on  the  hot  plate  at  a  nearly  boiling  temperature  for  some  time  to 
allow  any  tartaric  acid  carried  down  by  the  precipitate  to  dis- 
solve. This  is  important. 

Now  allow  the  solution  to  cool  somewhat  and  filter,  preferably 
through  asbestos,  and  wash  a  half  dozen  times  with  warm  water. 
Set  a  clean  flask  under  the  funnel  (or  wash  out  the  suction  flask 
if  one  is  used)  and  pour  over  the  white  precipitate  30  c.c.  of  a  hot 
10  per  cent.,  solution  of  NaOH,  and  wash  well  with  water. 

Heat  the  filtrate  to  about. 50°  and  run  in,  slowly  at  first  and  with 
constant  stirring,  standard  permanganate  solution.  The  liquid 
being  titrated  turns  a  green  color.  After  an  amount  of  perman- 
ganate has  been  added  which  judging  from  the  amount  of  the 
CuCNS  which  was  obtained  is  about  half  the  amount  necessary 
to  finish  the  titration,  test  a  drop  for  sulfocyanic  acid  by  adding 
it  on  a  white  plate  to  a  drop  of  ferric  chloride  strongly  acid  with 
HC1.  If  a  deep  red  color  remains  after  stirring  the  drops,  con- 
tinue adding  the  permanganate  5  c.c.  at  a  time  until  a  test  gives 
a  slight  red  color,  then  test  after  every  2  c.c.  until  a  test  shows 
almost  no  red  indicating  the  absence  of  more  than  a  trace  of 


212  METALLURGICAL  ANALYSIS 

sulfocyanic  acid  ion.  Now  add  30  c.c.  of  1  : 1  H2S04,  stir  the 
solution  until  all  MnO2  dissolves  and  then  finish  the  titration  to 
the  usual  permanganate  end  color. 

Notes  on  Process. — If  the  ore  does  not  contain  lead  it  is  not  necessary 
to  filter  off  the  gangue.  If  it  does,  the  lead  sulfate  must  be  filtered  off, 
as  it  goes  into  solution  in  the  ammonium  tartarate  and  precipitates  as 
lead  sulfite  with  the  CuCNS.  Silver,  if  present  in  the  ore,  will  precipi- 
tate as  sulfocyanate  but  may  be  removed  as  AgCl  with  the  lead. 

The  tartaric  acid  keeps  antimony  in  solution.  Not  more  than  3  grams 
should  be  used  as  a  crystalline  compound  of  tartaric  acid  tends  to  sepa- 
rate from  the  solution  when  it  cools  if  too  much  is  present.  Hence  not 
too  much  should  be  used  and  the  solution  should  be  kept  hot. 

It  is  essential  that  the  precipitation  of  CuCNS  be  made  just  as  directed 
as  to  acidity,  stirring  and  digestion  after  precipitation. 

After  a  little  experience  it  is  easy  to  tell  how  much  permanganate  it  is 
safe  to  add  before  testing  for  sulfocyanic  acid.  But  it  does  no  harm 
to  begin  testing  from  the  first  after  each,  say,  5  c.c.  of  permanganate. 
One  can  tell  from  the  depth  of  the  red  color  obtained  on  testing  with 
ferric  chloride  when  one  is  nearing  the  end.  When  the  test  gives  almost 
no  red,  it  will  still  require  several  cubic  centimeters  of  permanganate  to 
finish  the  titration  when  the  solution  is  made  acid.  The  permanganate 
used  is  one  of  which  1  c.c.  equals  0.01  gram  of  iron  or  0.001897  gram  of 
copper. 

The  writer  prefers  to  filter  the  CuCNS  on  an  asbestos  mat  either  in  a 
Gooch  crucible  or  in  a  funnel  containing  a  plug  of  glass  wool,  on  which 
the  asbestos  fiber  is  sucked  down  tightly.  If  the  filtering  is  done 
through  paper  the  blank  is  increased.  A  blank  should  be  made  in  any 
case  to  determine  whether  the  NaOH  contains  oxidizable  impurities. 
The  blank  should  be  almost  nothing. 

When  the  permanganate  is  added  to  the  alkaline  solution  it  turns 
green;  on  standing  MnCh  separates  because  the  permanganate  is  reduced 
thus,  2  KMn04  =  K2Mn04-f-20.  The  oxygen  oxidizes  the  sulfocyanate. 

REFERENCE: 

DEMOREST,  J.  Ind.  Eng,  Chem.,  V,  p.  215. 

Very  excellent  results  can  be  obtained  by  dissolving  the  precipitate 
in  2  c.c.  of  strong  nitric  acid,  boiling  the  solution  for  a  few  minutes  to 
destroy  all  sulfocyanic  acid,  adding  NH4OH  until  the  solution  is  alka- 
line, then  making  acid  with  acetic  acid  and  determining  the  copper  by  the 
iodide  titration.  (See  TSUKAKOSKI,  Eng.  Mining  J.,  XC,  969).  This  is 
the  method  the  writer  prefers  on  miscellaneous  ore  samples. 


CHAPTER  XXII 

THE  DETERMINATION  OF  LEAD  IN  ORES 

Lead  may  be  determined  either  gravimetrically  or  volumetrically. 
The  electrolytic  method  is  the  most  accurate  one  and  is  quite  rapid. 
Lead  ores  are  dissolved  in  about  the  same  way  as  copper  ores.  The 
chief  minerals  are  galena  (PbS),  cerrusite  (PbC03),  anglesite  (PbS04). 

THE  ELECTROLYTIC  DETERMINATION  OF  LEAD 

Lead  is  precipitated  on  the  anode  from  a  nitric  acid  solution  as  Pb02. 
The  precipitation  is  rapid  owing  to  the  high  atomic  weight  of  lead  and 
the  small  solution  tension  of  Pb02  in  nitric  acid.  The  precipitated 
Pb02  does  not  adhere  well  to  a  smooth  flat  electrode,  but  adheres  well  to 
a  gauze  electrode,  so  well 'in  fact  that  it  cannot  be  rubbed  off  with  the 
finger. 

If  bismuth  or  antimony  are  present  they  will  partially  deposit  with 
the  lead,  and  manganese  will  also  deposit  as  Mn02  with  the  lead  unless 
the  solution  is  very  acid.  The  presence  of  arsenic,  selenium  or  tellurium 
will  prevent  the  precipitation  of  the  Pb02  partially  or  wholly.  If  any 
of  these  are  present  they  must  be  removed  by  chemical  means,  which  is 
easily  done.  Phosphoric  acid  if  present  will  prevent  the  precipitation  of 
lead. 

Process  of  Analysis  for  Ores  Free  from  Arsenic,  Antimony  or 
Bismuth. — Weigh  an  amount  of  sample  containing  not  more  than 
0.5  gram  of  lead.  Put  it  in  a  250  c.c.  beaker,  add  10  c.c.  of  strong 
HC1  and  heat  to  boiling  for  several  minutes.  Then  when  most 
of  the  sulphur  is  driven  off  as  H2S  add  15  c.c  of  HNO3  and  con- 
tinue the  heating  until  the  ore  is  all  decomposed  and  finally  boil 
vigorously  to  expel  all  chlorine.  There  must  be  no  chlorine  pres- 
ent during  the  electrolysis.  Add  20  c.c.  of  water  and  then 
NH4OH  until  there  is  considerable  excess  and  heat  until  any 
lead  sulfate  is  dissolved.  Then  add  HNO3  until  there  is  15  c.c. 
excess  present,  dilute  to  100  c.c.  and  electrolyze,  using  a  gauze 
anode.  With  a  cylindrical  gauze  anode  %  in.  in  diameter  and 

213 


214  METALLURGICAL  ANALYSIS 


in.  high  a  current  of  3  amperes  and  a  potential  of  about  3 
volts  will  cause  complete  deposition  in  15  minutes  to  a  half  hour. 
It  is  best  to  electrolyze  in  a  hot  solution. 

Break  the  current  and  set  the  anode  in  a  beaker  of  pure  water, 
then  remove  and  dry  at  a  temperature  of  230°  in  an  oven.  Cool 
and  weigh.  Multiply  the  Pb02  by  0.8640  to  get  the  weight  of  the 
lead. 

To  remove  the  PbO2  set  the  electrode  in  a  beaker  containing 
warm  1  :  3  HNO3  and  add  a  few  cubic  centimeters  of  alcohol  or 
formic  acid.  The  Pb02  is  reduced  to  PbO,  which  is  soluble  in 
nitric  acid. 

If  the  ore  is  soluble  in  nitric  acid,  the  HC1  may  be  dispensed 
with  and  the  sample  treated  directly  with  the  nitric  acid.  This 
will  cause  the  formation  of  considerable  lead  sulfate  which  will 
dissolve  when  the  solution  is  made  alkaline  and  heated. 

Method  for  Ores  Containing  Antimony  or  Bismuth.  —  Dissolve 
the  ore  as  above  directed  and  then  add  5  c.c.  of  sulfuric  acid  and 
evaporate  to  very  copious  fumes  of  H2SO4.  Gool  and  add  30  c.c. 
of  water  containing  3  grams  of  tartaric  acid  to  keep  the  antimony 
in  solution.  Heat  to  boiling  to  dissolve  all  soluble  salts,  cool, 
filter  and  wash  three  times  with  cold  water.  Wash  the  lead  sul- 
fate back  into  the  beaker  with  a  small  amount  of  water  and  pour 
through  the  filter  into  the  beaker  hot  ammonium  nitrate  solution 
made  by  adding  to  30  c.c.  of  1  :  1  nitric  acid  10  c.c.  NH4OH. 
This  will  dissolve  any  lead  sulfate  left  on  the  paper.  Digest  the 
solution  in  the  beaker  until  the  lead  sulfate  is  all  dissolved,  then 
add  nitric  acid  until  there  is  15  c.c.  excess  present,  heat  and  elec- 
trolyze as  above. 

To  test  the  purity  of  the  deposit  the  following  method  is  good  : 
Place  the  anode  in  a  beaker  containing  40  c.c.  of  1  :3  nitric  acid, 
add  a  few  cubic  centimeters  of  formic  acid  and  heat  until  all 
PbO2  is  dissolved.  Wash  the  anode,  catching  the  washings  in  the 
beaker,  add  5  c.c.  of  sulfuric  acid  and  evaporate  to  copious  fumes. 
Cool,  add  30  c.c.  of  water  and  heat  to  boiling  several  minutes  to 
change  any  lead  bisulfate  to  sulfate.  Cool,  add  5  c.c.  of  alcohol, 
allow  to  settle  and  filter  in  a  weighed  Gooch  crucible  and  wash 
several  times  with  10  per  cent,  alcohol.  Ignite  for  five  minutes  at 
a  barely  visible  red  over  a  Bunsen  burner.  Weigh  and  multiply 
the  weight  of  lead  sulfate  by  0.6830.  Ores  may  also  be  analyzed 


THE  DETERMINATION  OF  LEAD  IN  OREH  215 

in  this  way  if  the  analyst  prefers  to  weigh  lead  sulfate  instead  of 
Pb02.  That  is,  the  ore  is  dissolved  as  in  the  method  for  ores  free 
from  bismuth  and  electrolyzed.  Then  the  Pb02  (with  oxides  of 
bismuth  and  antimony  and  manganese  possibly)  is  dissolved  with 
nitric  and  formic  acids  and  evaporated  to  copious  fumes.  Thirty 
cubic  centimeters  of  water  are  then  added  and  boiled,  cooled, 
filtered  and  the  lead  sulfate  washed  with  10  per  cent,  alcohol. 
The  Gooch  crucible  and  the  precipitate  are  heated  for  five  minutes 
over  a  Bunsen  burner,  cooled  and  weighed.  No  elements  inter- 
fere and  very  good  results  are  obtained. 

REFERENCES: 

SMITH,  "Electro  Analysis." 

PERKIN,  "Practical  Methods  of  Electro-chemistry." 

BENNER  and  Ross,  "Electrolytic  Determination  of  Lead  in  Ores," 

Mining  Sci.  Press,  CI,  642. 
LIST,  Metal  Ghent.  Eng.,  X,  135. 
BENNER,  /.  Ind.  Eng.  Ghent.,  II,  348. 
WOICIECHOWSKI,  Met.  Ghent.  Eng.,  X,  108. 

For  the  determination  of  lead  by  the  molybdate  method  of 
Alexander  see  Low,  "  Technical  Methods  of  Ore  Analysis." 
This  method  is  less  reliable  and  no  more  rapid  than  the  dichro- 
mate  method  and  so  is  not  given  here. 

For  the  permanganate  method  for  lead,  see  BOLLENBACH, 
Chem.  Ztg.,  XXXIII,  1142. 

THE  VOLUMETRIC  CHROMATE  METHOD  FOR  LEAD 

The  following  method  is  the  one  devised  by  Guess  and  modified  by 
Low  and  Waddell.  Low  says,  "I  find  it  more  generally  satisfactory 
than  any  other." 

It  depends  upon  the  precipitation  of  lead  chromate  from  an  acetic 
acid  solution,  which  is  then  dissolved  in  hydrochloric  acid,  potassium 
iodide  added  and  the  liberated  iodine  titrated  with  standard  thiosulfate 
solution. 

Solutions  Required.  Extraction  Solution. — Make  a  cold  satu- 
rated solution  of  sodium  acetate  and  filter  it.  Dilute  it  with  2 
volumes  of  water  and  add  30  c.c.  of  80  per  cent,  acetic  a'cid. 

Hydrochloric  Acid  Mixture. — Make  a  cold  saturated  solution 
of  Nad  and  filter  it.  To  1  liter  of  the  salt  solution  add  250  c.c. 
of  water  and  100  c.c.  of  hydrochloric  acid,  sp.  gr.  1.2. 


216  METALLURGICAL  ANALYSIS 

Potassium  Bichromate. — Make  a  cold  saturated  solution  of  the 
commercial  salt  and  filter  it. 

Starch  Solution. — Make  as  directed  on  page  100. 

Process  of  Analysis. — Weigh  0.5  gram  of  the  ore  and  put  it 
into  a  150  c.c.  flask.  Add  10  c.c.  of  strong  HC1  and  heat  until  no 
more  H2S  comes  off.  Add  5  c.c.  nitric  acid  and  boil  until  the  ore 
is  completely  decomposed.  Now  add  10  c.c.  of  1: 1  sulfuric  acid 
and  boil  until  copious  white  fumes  come  off.  Cool,  add  50  c.c. 
of  water  and  heat  to  boiling  until  all  the  soluble  salts  are  dis- 
solved, cool  and  add  5  c.c.  of  ethyl  alcohol,  allow  to  settle,  then 
filter  through  a  9  cm.  filter  and  wash  with  cold  10  per  cent, 
sulfuric  acid  solution  five  times  and  then  twice  with  water. 

Have  the  extraction  solution  nearly  boiling,  and  with  a  fine  jet 
wash  the  lead  sulfate  back  into  the  flask,  then  wash  the  filter 
thoroughly  with  the  hot  solution  until  all  lead  sulfate  remaining 
on  it  is  dissolved,  catching  the  washings  in  the  flask  containing  the 
rest  of  the  lead  sulfate,  and  taking  care  to  wash  under  the  folds  of 
the  filter  paper.  Heat  the  filtrate  to  boiling  and  add  more  of  the 
acetate  solution  if  necessary  to  dissolve  all  of  the  lead  sulfate. 
Finally  dilute  to  150  c.c.,  heat  to  boiling,  add  10  c.c.  of  the 
dichromate  solution  and  boil  for  seven  minutes.  It  is  necessary 
to  boil  about  this  length  of  time  to  insure  always  the  same  con- 
stitution of  the  lead  chromate.  Now  filter  through  a  large  filter 
paper  and  wash  the  flask  and  precipitate  ten  times,  with  a  hot 
solution  of  sodium  acetate  made  by  diluting  50  c.c.  of  a  cold 
saturated  solution  to  1  liter.  Place  the  clean  flask  under  the 
funnel,  and  with  a  jet  of  the  cold  HC1  mixture  dissolve  the  pre- 
cipitate on  the  filter.  Continue  the  washing  and  stirring  up  the 
precipitate  with  the  HC1  mixture  until  all  the  residue  and  all 
color  are  removed  from  the  filter.  Use  at  least  50  c.c.  of  the 
mixture. 

Now  add  4  c.c.  of  a  25  per  cent,  solution  of  KI  and  titrate  at 
once  with  standard  sodium  thiosulfate  solution.  Continue  add- 
ing the  thiosulfate  until  the  brown  color  of  the  liberated  iodine  be- 
comes faint;  then  add  enough  starch  solution  to  produce  a  strong 
blue  color  and  continue  the  titration  until  the  solution  becomes  a 
pale  green  with  no  tinge  of  blue.  The  end  point  is  very  sharp. 

Standardize  the  thiosulfate  solution  on  pure  lead.  The 
reactions  in  the  determination  are: 


THE  DETERMINATION  OF  LEAD  IN  ORES      217 


2PbCrO4+2KC2H3O2+2HC2H3O2. 
=  6KCl+2CrCl3+8H2O+6I. 

2Na2S2O3+2I  =  2NaI  +  Na2S4O4. 

Therefore  one  Pb  equals  one  H2CrO4  which  liberates  31,  which 
equals  3Na2S2O3.  That  is,  to  titrate  the  iodine  liberated  by  the 
H2CrO4  from  one  Pb  requires  3Na2S2O3  •  5H2O.  Then  to  make  a 
solution  of  thiosulfate,  1  c.c.  of  which  will  equal  0.005  gram  of 
lead,  will  require  for  1  liter  the  amount  of  thiosulfate  indicated 
by  the  following  proportion:  Pb:3Na2S2O3-5H2O::X:5,  or 
17.985  grams  per  liter.  The  thiosulfate  solution  used  for  the 
copper  determination  will  do.  To  standardize,  dissolve  about 
0.2  gram  of  pure  lead  in  15  c.c.  of  1:2  nitric  acid,  add  5  c.c.  of 
sulfuric  acid  and  evaporate  to  strong  H2SO4  fumes  and  treat 
as  above  directed  for  an  ore. 

Notes  on  the  Process.  —  As  a  fungus  growth  forms  in  the  acetate  wash, 
only  enough  to  last  a  day  should  be  made  unless  it  is  heated  frequently. 

If  the  end  point  be  passed  in  titrating,  a  few  drops  of  a  standard 
dichromate  solution  may  be  added  and  the  titration  finished.  The  iron 
value  of  the  dichromate  multiplied  by  1.2363  gives  the  lead  value. 

The  constitution  of  the  lead  chromate  depends  upon  the  temperature, 
acidity  and  concentration  of  the  solution  and  the  precipitation  of  the 
lead  from  the  ore  must  be  made  exactly  as  it  is  made  in  the  standardiza- 
tion of  the  thiosulfate. 

Bismuth  in  small  amount  does  not  interfere  but  if  there  is  much  in  the 
sample  some  may  remain  as  sulfate  with  the  lead.  In  such  a  case  just 
before  filtering  off  the  lead  chromate  add  2  grams  of  citric  acid  dissolved 
in  a  little  hot  water.  This  will  dissolve  any  bismuth  chromate  present. 

If  the  ore  contains  barium  it  is  difficult  to  extract  all  the  lead  sulfate 
with  the  acetate  mixture.  In  such  a  case  after  the  acetate  has  been 
used,  drop  the  filter  in  a  flask,  add  10  c.c.  of  strong  HC1  and  boil  almost 
to  dryness,  add  25  c.c.  of  the  acetate  solution,  boil  vigorously  and  filter 
and  wash;  the  combined  filtrates  are  then  treated  as  usual. 

Wilder'  s  Modification.  —  Treat  0.50  gram  of  ore  as  is  usual'  for 
lead  ores  up  to  the  point  where  the  washed  sulfate  is  obtained  on 
the  filter  paper.  Remove  the  paper  from  the  funnel  and  fold 
lengthwise  in  such  a  manner  that  it  can  be  introduced  into  a  200 
c.c.  graduated  flask.  Place  a  few  grams  of  sodium  acetate  and 
1  c.c.  of  acetic  acid  in  the  flask  and  add  about  50  c.c.  of  water. 
Then  place  the  flask  on  the  hot  plate  until  the  lead  sulfate  is  all  in 


218  METALLURGICAL  ANALYSIS 

solution.  This  may  be  hastened  by  shaking  to  break  up  the 
filter  paper. 

Now  run  in  an  excess  of  standard  dichromate  solution  from  a 
burette,  and  after  mixing  by  shaking,  make  the  contents  up  to  the 
mark  by  adding  water.  Invert  the  flask  ten  times  with  the  hand 
over  its  mouth  to  mix  thoroughly.  Take  three  No.  589  S.  &  S. 
filters,  fold  as  one  and  place  in  a  dry  funnel  with  a  dry  100  c.c. 
flask  beneath.  Filter  100  c.c.  and  transfer  to  an  Erlenmeyer 
flask. 

Add  a  few  cubic  centimeters  of  sulfuric  acid,  enough  potassium 
iodide  to  react  with  the  excess  of  chromic  acid  and  titrate  with 
sodium  thiosulfate  in  the  usual  manner,  using  starch  indicator. 
The  standard  dichromate  contains  3.558  grams  of  dichromate  per 
liter.  The  thiosulfate  theoretically  contains  8.8177  grams  per 
liter,  but  9.150- will  be  more  apt  to  give  the  desired  strength. 

Making  the  solutions  this  way,  1  c.c.  of  dichromate  should 
equal  1  per  cent,  of  lead  and  2  c.c.  of  thiosulfate.  Therefore 
subtracting  the  cubic  centimeters  of  thiosulfate  used  from  the 
cubic  centimeters  of  dichromate  used  will  give  the  per  cent,  of 
lead  direct,  without  any  further  calculation. 

Notes  on  the  Method. — The  chromate  solution  and  the  thiosulfate 
solution  are  both  stable,  and  once  standardized  will  not  require  further 
attention  for  a  month  or  more.  They  may  be  titrated  against  each 
other  occasionally  and  restandardized  if  any  variation  is  found. 

The  lead  chromate  precipitate  is  fine  unless  boiled,  and  therefore 
three  filter  papers  are  used.  The  solution  filters  quickly,  however.  In 
methods  where  the  solution  is  boiled  the  lead  chromate  is  of  variable 
composition,  depending  upon  the  conditions  of  precipitation,  basic 
chromates  being  formed.  This  method  avoids  any  washing  of  the 
chromate  and  thus  saves  time  and  avoids  errors  due  to  washing. 

REFERENCES: 

Low,  " Technical  Methods  of  Ore  Analysis." 
GUESS,  Trans.  Am.  Inst.  Mining  Engrs.,  XXXV,  359. 
WADDELL,  J.  Ind.  Eng.  Chem.,  Ill,  638. 
WILDER,  Eng.  Mining  J.,  XCII,  390. 


CHAPTER  XXIV 
THE  DETERMINATION  OF  TIN  IN  ORES 

Tin  occurs  in  ores  generally  as  SnC>2  (Cassiterite),  sometimes  as 
(Stannite).  Cassiterite  is  insoluble  in  all  acids,  and  to  get  the  tin  in 
solution  it  is  necessary  either  to  fuse  the  ore  with  an  alkali,  forming  a 
stannate  which  is  soluble  in  acids  or  to  reduce  the  Sn02  at  an  elevated 
temperature  with  either  a  reducing  gas  as  illuminating  gas  or  with  finely 
divided  metal  as  powdered  zinc  or  aluminium.  When  the  amount  of  tin 
is  very  low  and  a  large  sample  is  used,  the  reduction  of  the  Sn(>2  with  a 
powdered  metal  to  metallic  tin  followed  by  solution  of  the  tin  in  hydro- 
chloric acid  is  best,  because  if  a  large  sample  is  fused  with  an  alkali  and 
the  fusion  dissolved  in  acid,  the  liberated  silicic  acid  causes  trouble  in 
filtration.  A  solution  of  stannic  chloride  in  hydrochloric  acid  should 
not  be  evaporated  as  stannic  chloride  boils  at  114°C. 

Tin  may  be  determined  gravimetrically  by  weighing  as  SnO2  after 
precipitation  as  metastannic  acid,  or  by  weighing  as  the  metal  after 
electrolytic  precipitation,  or  volumetrically  by  titrating  the  tin  in 
stannous  state  by  a  standard  oxidizing  solution,  preferably  iodine. 

Stannous  salts  take  up  oxygen  really  from  the  air,  consequently  the 
solution,  which  is  to  be  titrated,  must  be  protected  from  the  air  by  a  neu- 
tral gas  as  carbon  dioxide. 

The  following  process  is  the  well-known  one  of  Pierce  and  Low  with  the 
reduction  and  titration  carried  out  as  directed  by  Patrick  and  Wilsnack. 
It  depends  upon  reducing  the  tin  in  a  strong  hydrochloric  acid  solution  in 
absence  of  air  by  means  of  the  combined  action  of  metallic  iron  and  anti- 
mony. The  tin  is  reduced  to  SnCls,  which  is  then  titrated  with  iodine 
solution,  thus,  SnCl2+2I-f  2HCl  =  SnCl4+2HI. 

Process  of  Analysis. — Place  in  an  iron  crucible  about  8  grams 
of  sodium  hydroxide  or  5  grams  of  sodium  peroxide  and  heat  over 
a  Bunsen  burner  until  the  charge  is  melted.  Cool  and  add  a 
gram  of  the  finely  ground  ore.  Cover  the  crucible  and  heat 
cautiously  to  prevent  spattering  and  finally  heat  with  the  full 
flame  of  the  Bunsen  until  the  fusion  is  quiescent  and  keep  the 
mass  Ilius  fused  for  about  a  half  hour  to  insure  complete  solution 
of  the  cassiterite.  Cool  and  dissolve  the  cake  in  about  50  c.c.  of 

219 


220  METALLURGICAL  ANALYSIS 

water  and  enough  HC1  to  neutralize  all  the  NaOH  and  add  50  c.c. 
additional.  When  all  is  in  solution,  transfer  the  solution  to  a 
500  c.c.  Erlenmeyer  flask  and  add  5  c.c.  of  sulfuric  acid  in  which 
is  dissolved  0.1  gram  of  antimony. 

Close  the  flask  with  a  three-hole  rubber  stopper.  Through 
one  hole  put  a  piece  of  glass  tubing  reaching  to  the  bottom  of 
the  flask,  through  another  place  an  iron  rod  the  end  of  which  is 
coiled  into  a  spiral.  The  rod  should  fit  loosely  enough  to  slip 
up  and  down  in  the  hole  in  the  stopper,  and  be  long  enough  to 
have  the  spiral  reach  to  the  bottom  of  the  flask  while  the  other 
end  sticks  out  of  the  stopper  several  inches. 

Push  the  iron  spiral  down  in  the  solution  and  pass  CC>2  or 
natural  gas  (freed  from  H2S  by  passing  through  NaOH)  through 
the  glass  tube  until  the  air  is  driven  out  of  the  flask  and  then 
boil  the  solution  for  25  minutes  while  continuing  the  current  of 
gas.  Cool  the  flask  while  a  rapid  current  of  gas  passes  through 
to  prevent  air  entering.  When  the  solution  is  cold  raise  the 
iron  coil  out  of  the  liquid,  wash  it  by  squirting  a  jet  of  recently 
boiled  cold  water  through  the  third  hole  in  the  stopper,  put  in 
4  c.c.  of  starch  solution  and  then  titrate  the  tin  with  standard 
iodine  solution  by  introducing  the  tip  of  the  burette  through  the 
hole  in  the  rubber  stopper  and  running  in  the  iodine  solution 
until  a  drop  turns  the  starch  blue.  The  iron  coil  must  be  so 
placed  that  the  iodine  solution  does  not  drop  on  it. 

Notes  on  the  Process. — When  near  the  end  point,  which  is  told  by 
the  slow  disappearance  of  the  blue  color  of  starch  iodide,  the  titration 
should  proceed  slowly  to  prevent  overrunning  the  end  point. 

Large  amounts  of  copper,  lead,  nickel,  and  perhaps  other  metals  inter- 
fere with  the  accuracy  of  the  titration  if  they  are  present  and  ores  con- 
taining them  should  be  first  treated  with  aqua  regia,  evaporated  to 
dryness,  digested  with  hydrochloric  acid  and  filtered.  The  residue  on 
the  paper  is  then  treated  for  tin  as  above  directed. 

Arsenic  and  antimony  when  in  trivalent  condition  consume  iodine  if 
the  solution  is  weakly  acid  but  in  the  strong  acid  solution  as  used  in  this 
process  they  are  without  effect. 

The  reduction  of  the  tin  is  not  complete  if  only  iron  is  used  or  if  only 
antimony  is  used  but  is  perfect  if  both  are  used. 

Iodine  Solution. — To  make  the  iodine  solution,  put  20  grams 
of  KI  and  50  c.c.  of  water  in  a  liter  flask  and  then  add  12.7  grams 


THE  DETERMINATION  OF  TIN  IN  ORES  221 

of  pure  iodine,  stopper  the  flask  and  shake  the  solution  until  the 
iodine  is  all  dissolved.  Then  dilute  to  a  liter  and  mix  well. 
Standardize  against  c.p.  tin,  by  dissolving  0.2  gram  in  a  flask  in 
50  c.c.  water  and  50  c.c.  strong  HC1.  When  dissolved  add  5  c.c. 
of  sulfuric  acid  containing  0.15  gram  of  antimony  and  reduce 
and  titrate  as  directed  for  the  ore.  Iodine  solution  of  the  above 
strength  is  tenth-normal  and  should  equal  0.00595  gram  of  tin 
per  cubic  centimeter. 

The  results  obtained  are  accurate  to  0.2  per  cent,  when  as  much 
as  0.5  gram  of  tin  is  present  and  much  more  accurate  with  the 
small  amounts  of  tin  found  in  ores. 

REFERENCES: 

Low,  "Technical  Methods  of  Ore  Analysis,"  p.  247. 
PATRICK  and  WILSNACK,  J.  Am.  Chem.  Soc.,  IV,  597. 
GRAY,  J.  Chem.  Mel.  S.  Africa,  X,  312. 
MORGAN,  Chem.  Eng.,  XIV,  289. 

LEWIS,  London  Mining  J.,  1911,  606,  J.  Chem.  Met.  S.  Africa,  XII, 
32.     The  electrolytic  determination  of  tin. 


CHAPTER  XXV 
THE  ANALYSIS  OF  REFINED  COPPER 

The  properties  of  copper  are  greatly  affected  by  the  presence  of  small 
amounts  of  impurities.  The  most  common  impurities  are  arsenic,  anti- 
mony, oxygen,  bismuth,  lead,  iron,  sulfur.  Also  silver  and  gold  are  often 
present  in  considerable  amounts,  while  silicon,  aluminium,  nickel,  cobalt, 
selenium,  phosphorus  and  tellurium  may  be  present. 

The  following  method  for  arsenic  and  antimony  is  as  described  by 
Heath.1  It  depends  upon  the  precipitation  of  the  antimony  and  arsenic 
from  the  solution  of  the  copper  by  adding  a  sufficient  amount  of  ferric 
salt  and  then  NH4OH.  The  ferric  hydroxide  carries  down  with  it  the 
arsenic  and  antimony  in  combination  with  the  iron.  The  arsenic  and 
antimony  are  separated  from  the  iron  by  hydrogen  sulfide,  the  sulfides 
are  dissolved  in  sodium  sulfide,  the  arsenic  and  antimony  oxidized  to 
pentavalent  form  by  fuming  nitric  acid.  Arsenic  is  separated  from 
antimony  by  precipitating  it  out  as  sulfide  from  2  : 1  hydrochloric 
acid  solution  in  which  antimony  sulfide  is  soluble. 

Process  of  Analysis. — Dissolve  25  grams  of  the  drillings  in  a 
600  c.c.  beaker  with  110  c.c.  of  nitric  acid,  sp.  gr.  1.42.  Dilute 
to  300  c.c.  and  add  a  solution  of  2  grams  of  c.p.  ferric  sulfate 
made  from  c.p.  crystallized  ferrous  sulfate.  Heat  nearly  to  boil- 
ing and  add  NH4OH  until  the  iron  is  precipitated  and  the  copper 
salts  redissolved.  This  will  take  about  175  c.c.  Heat  to  boil- 
ing, let  settle  a  half  hour  on  a  hot  plate  and  filter  on  a  15  cm. 
ashless  paper.  If  bismuth  is  to  be  determined  add  2  grams  of 
ammonium  carbonate  and  5  c.c.  of  saturated  sodium  phosphate 
solution  after  the  iron  is  precipitated.  If  the  copper  contains 
more  than  0.1  per  cent,  of  arsenic  and  antimony  add  more  of 
the  ferric  sulfate  to  the  acidified  filtrate  and  again  precipitate 
with  NH4OH,  filter  and  wash  both  precipitates  well  with  hot 
1:10  NH4OH.  Redissolve  the  precipitate  or  precipitates  with 
dilute  sulfuric  acid,  precipitate  again  with  NH4OH,  filter  and 
wash  well. 

1  HEATH,  J.  Am.  Chem.  Soc.,  Ill,  74. 

222 


THE  ANALYSIS  OF  REFINED  COPPER  223 

Dissolve  the  ferric  hydroxide  with  hot  dilute  sulfuric  acid  con- 
taining 5  per  cent,  of  hydrochloric  acid  and  precipitate  in  the 
cold  the  arsenic,  antimony  and  bismuth  with  hydrogen  sulfide, 
passing  the  gas  through  for  15  minutes.  Stopper  the  flask  and 
let  settle  over  night.  In  the  morning  pass  hydrogen  sulfide 
through  again,  filter  on  a  small  filter  paper  and  wash  with  slightly 
acid  hydrogen  sulfide  water. 

Transfer  the  paper  and  contents  to  a  small  beaker  and  dissolve 
the  sulfides  of  antimony,  arsenic  and  tin  with  hot  sodium  sulfide, 
digesting  until  they  are  all  dissolved.  Use  as  little  sodium  sul- 
fide as  possible.  Filter  and  wash  with  slightly  alkaline  hydrogen 
sulfide  water.  Bismuth  sulfide  remains  on  the  filter. 

To  the  filtrate  add  0.2  gram  of  sodium  hydroxide,  evaporate 
to  dryness  on  a  steam  plate,  treat  the  residue  with  20  c.c.  of 
strongest  fuming  nitric  acid  and  digest  until  the  sulfur  is  all  dis- 
solved. Evaporate  to  dryness  again. 

Dissolve  the  residue  in  35  c.c.  of  hydrochloric  acid  containing 
two  parts  of  hydrochloric  acid,  sp.  gr.  1.2,  to  one  of  water,  adding 
a  crystal  of  tartaric  acid.  Pass  hydrogen  sulfide  through  the 
cold  solution  until  the  solution  is  saturated,  whereupon  the  arsenic 
precipitates.  Allow  to  settle  a  short  time,  filter  on  an  asbestos 
mat,  and  wash  with  acid  of  the  same  strength  as  the  solution. 
Wipe  out  any  sulfide  adhering  to  the  side  of  the  beaker  with 
asbestos.  As  soon  as  the  mat  is  washed  well  the  beaker  is  re- 
moved and  the  acid  removed  from  the  mat  with  H2S  water. 
Test  the  filtrate  with  more  hydrogen  sulfide  gas.  Keep  the 
filtrate  for  the  antimony. 

Digest  the  mat  with  the  sulfides  in  a  small  beaker  with  fum- 
ing nitric  acid,  dilute  with  one  and  one-half  times  its  volume 
of  water  and  filter,  wash,  and  evaporate  to  dryness  with  0.1  to 
0.5  gram  of  sodium  nitrate  according  to  the  amount  of  arsenic 
present. 

Dissolve  the  residue  in  5  c.c.  of  cold  water,  10  drops  of  hydro- 
chloric acid  and  0.1  gram  of  tartaric  acid.  Filter  through  a  small 
paper  and  wash  with  the  smallest  amount  of  water  possible. 
Make  slightly  alkaline  with  NH4OH,  when  the  volume  should  not 
be  more  than  12  c.c.  Add  3  c.c.  of  magnesia  mixture,  make  up  to 
20  c.c.  with  strong  NH4OH  and  stir  five  minutes.  If  the  amount 


224  METALLURGICAL  ANALYSIS 

of  arsenic  is  excessive  add  more  precipitant  and  increase  the  vol- 
ume to  30  c.c.,  one-third  of  which  is  NH4OH. 

Allow  to  stand  over  night  in  a  cool  place,  filter  on  a  3  cm. 
filter  paper  and  wash  with  a  fine  jet  of  1:3  NH4OH  until  free 
from  chlorine.  Dry  the  paper  -in  an  oven,  crumble  out  the 
arsenate  on  a  glazed  paper  and  put  the  paper  in  a  porcelain  cruci- 
ble. Add  a  few  drops  of  saturated  ammonium  nitrate  and  char 
the  paper  very  carefully,  add  more  nitrate  and  again  heat  care- 
fully until  the  paper  is  consumed  without  giving  an  odor  of  arse- 
nic. Add  the  rest  of  the  arsenate,  ignite  at  a  full  red  heat  and 
weigh.  Or  filter  the  arsenate  on  a  small  weighed  Gooch  filter, 
wash  well,  ignite  and  weigh  as  Mg2As207,  which  contains  48.27 
per  cent.  As. 

The  magnesia  mixture  should  be  free  from  lime  and  should 
not  be  used  after  it  has  attacked  the  glass  of  the  bottle.  It  is 
made  of  one  part  of  magnesium  sulfate,  four  of  ammonium  chlo- 
ride, eight  of  water  and  four  of  ammonia,  sp.  gr.  0.90. 

Instead  of  determining  the  arsenic  gravimetrically  it  may  be 
titrated.  Transfer  the  solution  of  arsenic  sulfide  in  fuming  nitric 
acid  to  a  Kjeldahl  flask,  add  15  c.c.  sulfuric  acid  and  3  grams 
KHS04  and  evaporate  to  fumes  for  15  minutes.  Cool,  add  0.5 
tartaric  acid  and  fume  until  colorless.  Cool,  dilute  to  200  c.c. 
and  add  NH4OH  until  just  alkaline,  then  make  just  acid,  add 
3  drops  of  10  per  cent.  KI  and  10  grams  NaHCO3,  cool  and  titrate 
with  iodine.  The  solution  is  made  as  directed  on  page  225. 

Antimony. — The  filtrate  from  the  arsenic  sulfide  contains  the 
antimony  (and  traces  of  tin).  Evaporate  nearly  to  dryness  to 
remove  the  excess  of  acid,  dilute  to  25  c.c.  and  precipitate  the 
antimony  (and  tin)  with  H2S.  Filter,  dissolve  with  a  little 
sodium  sulfide  (to  remove  traces  of  copper),  filter  again,  make 
the  filtrate  acid  and  pass  in  H2S.  Filter  on  a  weighed  Gooch 
filter,  wash  with  H2S  water,  ignite  and  weigh  as  Sb204. 

If  the  determination  of  tin  is  desired  it  is  separated  from  the 
antimony  in  the  filtrate  from  the  arsenic  sulfide  by  Clark's  oxalic 
acid  method. 

Bismuth. — The  sulfide  of  bismuth  left  after  the  treatment  of 
sulfides  of  arsenic  and  antimony  with  Na2S  is  digested  with  10 
c.c.  of  nitric  acid  until  dissolved,  filtered,  1  c.c.  of  sulfuric  acid 
added  and  evaporated  to  strong  fumes  to  expel  all  nitric  acid. 


THE  ANALYSIS  OF  REFINED  COPPER  225 

Dilute  to  50  c.c.,  add  sulfurous  acid  and  10  c.c.  of  dilute  KI  solu- 
tion, boil  off  any  free  iodine,  filter  if  necessary  and  dilute  to  100  c.c. 
in  a  graduated  flask.  According  to  the  depth  of  color  take  10 
c.c.,  20  c.c.  or  50  c.c.  and  transfer  to  a  Nessler  tube.  Add  a  few 
cubic  centimeters  of  dilute  sulfurous  acid.  Into  another  tube 
put  as  much  KI  solution  as  in  the  assay  tube,  add  sulfurous 
acid  and  then  dilute  to  within  a  few  cubic  centimeters  of  the 
same  bulk.  Then  add  standard  bismuth  solution  until  the  tints 
are  the  same.  The  color  is  due  to  the  formation  of  bismuth  iodide. 

The  standard  bismuth  solution  is  made  as  follows:  Dissolve 
0.1  gram  of  bismuth  in  a  few  drops  of  nitric  acid,  evaporate  to 
fumes  with  2  c.c.  of  sulfuric  acid  and  dilute  to  1  liter.  The  sul- 
furous acid  used  is  made  by  diluting  10  c.c.  of  commercial  acid 
to  1  liter. 

One  must  be  careful  not  to  confuse  the  yellow  color  of  free 
iodine  with  that  of  bismuth  iodide.  If  the  yellow  color  is 
removed  by  boiling  and  returns  on  standing  it  is  due  to  free 
iodine.  Hence  the  necessity  of  having  a  little  sulfurous  acid 
present  to  remove  the  iodine.  But  a  strong  solution  of  sulfurous 
acid  will  liberate  iodine  in  the  presence  of  H2SO4. 

There  should  not  be  more  than  1  mg.  of  bismuth  in  the  tube  or 
less  than  0.1  mg.  No  elements  interfere. 

Selenium  and  Tellurium. — If  these  are  wanted  they  are  pre- 
cipitated before  the  arsenic,  antimony,  and  bismuth  by  passing 
S02  through  the  acid  solution.  This  precipitates  out  the  elemen- 
tary selenium  and  tellurium.  Filter  them  on  a  small  Gooch  mat, 
wash  with  water  containing  a  little  HC1  and  SC>2,  dry  at  104°C., 
weigh,  ignite  and  weigh  again. 

Starch  Indicator. — Starch  prepared  as  follows  is  much  more 
sensitive  to  iodine  than  when  prepared  in  the  ordinary  way. 
When  this  indicator  is  used  it  is  more  accurate  to  titrate  arsenic 
than  to  weigh  it. 

Allow  the  raw  starch  to  stand  for  24  hours  in  very  dilute  HC1, 
filter,  wash,  dry  for  three  hours  in  an  oven  at  100°C.  Boil  1 
gram  with  100  c.c.  of  water  and  filter. 

Iodine  Solution. — Dissolve  3.386  grams  of  pure  iodine  in  7 
grams  of  KI  and  a  little  water  and  dilute  to  1  liter.  The  end 
point  in  the  titration  is  clearer  if  three  drops  of  a  10  per  cent, 
solution  of  KI  are  added  after  the  NaHCO3. 

15 


226  METALLURGICAL  ANALYSIS 

Lead,  Iron,  Nickel,  Cobalt  and  Zinc. — Dissolve  50  grams  of 
the  copper  in  a  mixture  of  80  c.c.  sulfuric  acid,  50  c.c.  nitric  acid 
and  400  c.c.  of  water.  Dilute  to  600  c.c.  and  precipitate  the 
copper  on  a  large  perforated  platinum  cylinder,  using  an  11X11 
cm.  cathode  and  a  current  of  3  amperes  and  preferably  a  rotating 
anode  or  a  solenoid  to  rotate  the  solution.  When  the  copper  is  all 
deposited,  as  shown  by  a  test  of  a  few  cubic  centimeters  on  a  white 
plate  with  H2S,  evaporate  the  solution  to  a  small  volume,  then 
transfer  to  a  casserole  and  heat  to  fumes  to  remove  the  free  sul- 
furic acid  and  most  of  the  ammonium  salts.  The  residue  is  dis- 
solved in  water  and  any  lead  sulfate  and  silica  are  filtered  off. 
Hydrogen  sulfide  is  then  passed  through  the  acidified  filtrate  and 
the  precipitate  filtered  off  and  washed  with  hydrogen  sulfide 
water.  The  precipitate  is  extracted  with  a  little  hot  dilute  so- 
dium sulfide  and  the  residue  combined  with  the  other  precipitates 
containing  lead,  and  the  lead  determined  in  them  by  electrolysis 
including  the  lead  originally  deposited  on  the  anode  as  peroxide. 

The  main  solution  (volume  about  50  c.c.)  is  oxidized  and  the 
iron  precipitated  with  NH4OH.  Aluminium  of  course  also 
precipitates. 

The  filtrate  is  acidified  with  acetic  acid  and  1  c.c.  of  strong 
acetic  acid  is  added  in  excess.  Heat  to  boiling  and  pass  hydrogen 
sulfide  through.  Filter  off  the  ZnS,  ignite  and  weigh  as  oxide. 
Make  the  filtrate  alkaline  with  NH4OH  and  precipitate  the  nickel 
and  cobalt  with  H2S,  filter  and  ignite  and  weigh  as  oxides. 
Nickel  and  cobalt  may  be  separated  with  dimethylglyoxime. 
(See  page  138  et  seq.) 

DETERMINATION  OF  GASES  IN  COPPER 

Pure  CO  2  has  no  chemical  action  on  red  hot  copper.  If  copper 
drillings  are  heated  red  hot  in  a  current  of  pure  CO 2,  the  occluded  gases 
are  driven  out  and  the  loss  in  weight  is  the  weight  of  these  gases  which 
were  in  the  sample.  If  the  sample  is  then  heated  in  a  stream  of  hydro- 
gen, the  combined  oxygen  in  the  copper  is  driven  out  in  the  form  of  water, 
but  some  hydrogen  remains  in  the  copper.  This  may  then  be  driven 
out  by  igniting  again  in  a  stream  of  CO2  and  the  loss  in  weight  is  oxygen 
and  sulfur.  The  sulfur  driven  off  is  determined  by  passing  the  hydrogen, 
after  it  leaves  the  tube,  into  cadmium  chloride  solution  and  then  titrat- 
ing with  iodine  solution. 


THE  ANALYSIS  OF  REFINED  COPPER,  227 

Process. — Produce  CO2  in  a  generator  from  pure  sodium  bicar- 
bonate, or  marble,  and  HC1.  Purify  the  COz  by  passing  it 
through  a  train  of  the  following  reagents:  (A)  Saturated  KMnO4 
solution.  (B)  Solution  of  silver  sulfate.  (C)  Concentrated 
sulfuric  acid.  (D)  A  tube  of  dry  chromous  chloride.  (E) 
Stick  phosphorus.  (F)  Calcium  chloride.  (G)  Phosphorus  pent- 
oxide.  Also  make  pure  hydrogen  in  a  Kipp  generator  and  purify 
the  hydrogen  by  the  following  train:  (A)  KOH  solution.  (B) 
Strong  sulfuric  acid.  (C)  Palladiumized  asbestos  tube  heated 
red  hot.  (D)  Soda-lime.  (E)  Calcium  chloride.  (F)  Phos- 
phorus pentoxide.  The  exit  ends  of  the  CC>2  train  and  the 
hydrogen  train  should  be  connected  to  a  "T"  tube,  to  the  other 
end  of  which  is  attached  the  ignition  tube. 

Put  50  grams  of  fine  drillings  in  the  ignition  tube  and  weigh 
the  tube  and  drillings.  Attach  the  tube  to  the  "T"  and  pass 
CO2  through  until  all  the  air  is  driven  out  (about  30  minutes). 
Then  heat  the  tube  red  hot  for  30  minutes  while  a  rapid  stream 
of  C(>2  is  passing.  Cool  the  tube,  without  stopping  the  CO2,  and 
when  cool  displace  the  COz  with  air  by  aspirating  air  through. 
Weigh.  The  loss  in  weight  is  occluded  gases. 

Again  connect  the  ignition  tube  to  the  "T"  and  pass  in  hydro- 
gen for  15  or  more  minutes,  then  keep  at  a  red  heat  for  an  hour  or 
more,  depending  on  the  fineness  of  the  drillings.  The  exit 
hydrogen  must  be  passed  through  an  ammoniacal  CdCl2  solu- 
tion. After  the  hydrogen  has  been  passed  through  long  enough, 
shut  it  off  and  pass  the  CC>2  through  the  tube  until  the  hydrogen  is 
all  displaced  (at  least  20  minutes).  Cool  the  tube  and,  when  cool, 
displace  the  CO2  with  air  and  weigh.  The  loss  in  weight  is 
oxygen  plus  sulfur.  Titrate  the  sulfur  with  iodine  as  directed  on 
page  105.  Subtract  the  weight  of  sulfur  from  the  loss  in  weight 
to  get  the  weight  of  oxygen  in  the  sample. 

Great  care  must  be  used  to  have  the  surface  of  the  copper 
from  which  the  drillings  are  taken  perfectly  clean  and  free  from 
grease,  etc. 

The  H2O  found  may  be  caught  in  P2O5  and  weighed.  See 
determination  of  oxygen  in  steel,  page  181. 

REFERENCES: 

HEATH,  J.  hid.  Eng.  Chem.,  IV,  402. 

KELLER,  Trans.  Am.  Inst.  Mining  Eng.,  XLVI,  764  (1914). 

BROWNSON,  Trans.  Am.  Inst.  Mining  Eng.,  XLVI,  757  (1914). 


228  METALLURGICAL  ANALYSIS 

Sulfur. — The  only  rapid  and  exact  method  which  has  appeared 
in  print  for  the  estimation  of  traces  of  sulfur  in  the  refined  product 
is  the  following,  which  depends  upon  the  removal  of  the  copper 
from  its  solution  in  pure  nitric  acid  by  electrolysis.  The  solution, 
freed  from  copper,  is  gradually  transferred  to  a  No.  3  A  casserole 
and  evaporated  to  dryness  over  an  alcohol  flame  with  the  addition 
of  a  little  sodium  carbonate  to  retain  the  sulfuric  acid.  The 
remaining  nitric  acid  is  removed  by  two  evaporations  with  hydro- 
chloric acid.  A  little  HC1  and  25  c.c.  of  water  are  added  and  the 
solution  filtered.  If  any  lead  sulfate  is  found  on  the  filters,  they 
are  boiled  with  a  little  sodium  carbonate  to  render  the  sulfuric 
acid  soluble,  and  filtered.  The  filtrates  are  combined  and  are 
then  ready  for  precipitation  by  barium  chloride.  A  blank  analy- 
sis must  be  run  with  the  acids  and  distilled  water,  which  will 
usually  show  about  1  mg.  of  barium  sulfate.  When  the  copper 
contains  much  sulfur,  it  is  necessary  to  use  aqua  regia  for  its 
solution,  and  to  remove  the  hydrochloric  acid  by  subsequent 
evaporations  with  nitric  acid. 

REFERENCE: 

PRICE  and  MEAD,  "Brass  Analysis." 


CHAPTER  XXVI 
ANALYSIS  OF  REFINED  LEAD 

Process  of  Analysis. — Clean  100  grams  of  lead,  and  hammer  or 
roll  into  thin  plates,  being  very  careful  to  use  a  perfectly  clean  and 
bright  hammer  and  anvil  to  avoid  introducing  iron  into  the  sam- 
ple. Dissolve  the  lead  in  a  large  beaker  on  the  hot  plate  in  100 
c.c.  nitric  acid,  sp.  gr.  1.42,  and  250  c.c.  water.  If  the  solution 
gets  too  hot,  it  will  foam  very  much  and  run  over,  consequently  it 
is  necessary  to  watch  it  until  most  of  the  lead  is  dissolved.  For 
the  same  reason,  hammering  or  rolling  the  lead  into  very  thin 
strips  is  not  desirable. 

After  all  the  lead  is  dissolved  the  solution  is  generally  perfectly 
clear,  although  if  more  than  0.02  to  0.03  per  cent,  of  antimony  or 
tin  is  present  it  will  show  some  turbidity.  Dilute  the  solution  to 
nearly  500  c.c.  to  prevent  lead  nitrate  from  crystallizing  out  on 
cooling.  If  not  perfectly  clear,  filter.  Add  30  c.c.  concentrated 
sulfuric  acid  previously  diluted  with  water,  and  shake  the  flask. 
After  settling,  pour  off  the  clear  solution  and  wash  the  precipitate 
several  times  by  decantation. 

Evaporate  the  solution  to  fumes  of  H2S04,  take  up  with  50  c.c. 
of  water  and  filter  off  the  lead  sulfate  through  the  paper  contain- 
ing antimony  and  tin.  Digest  the  lead  sulfate  with  pure  sodium 
sulfide  solution,  filter  and  add  the  other  sodium  sulfide  solution 
obtained  further  on.  Treat  the  filtrate  from  the  lead  sulfate, 
while  hot,  with  H2S  for  some  time  and  pass  the  gas  through  until 
cold.  After  settling  completely,  filter,  determine  the  iron  and 
zinc  in  the  filtrate,  and  treat  the  sulfides  with  Na2S.  Determine 
antimony  and  arsenic  as  described  under  copper  analysis. 

The  insoluble  sulfides  of  lead,  bismuth,  copper,  and  silver  may 
be  dissolved  in  nitric  acid,  neutralized  with  sodium  carbonate, 
and  KCN  added.  Filter  off  lead  and  bismuth  carbonates,  acidify 
the  filtrate  with  H2SO4  under  the  hood,  filter  off  the  AgCN  and 
boil  the  solution  to  expel  all  HCN,  after  which  determine  the 
copper  in  the  solution  as  follows: 

229 


230  METALLURGICAL  ANALYSIS 

Nearly  neutralize  the  solution  with  NH4OH,  keeping  the  bulk 
small,  say  50  c.c.,  add  ammonium  acetate,  and  divide  into  two 
equal  parts.  Add  to  one-half  a  fair  excess  of  potassium  ferro- 
cyanide  solution,  and  filter  off  the  red  precipitate  immediately, 
passing  through  the  paper  twice  if  necessary.  Add  1  c.c.  acetic 
acid  to  each  and  the  same  amount  of  potassium  ferrocyanide  to 
the  unfiltered  half,  and  match  the  color  in  the  filtered  half  by 
adding  a  weak  copper  sulfate  solution  of  known  strength  from  a 
burette,  allowing  one  minute  between  each  addition  of  copper 
sulfate  for  the  color  to  develop. 

REFERENCE : 

CROOK'S  "Select  Methods  of  Chemical  Analysis,"  p.  338. 

'The  silver  cyanide  precipitate  is  not  desired,  for  silver  is 
determined  by  cupelling  a  separate  sample  of  the  lead. 

To  determine  bismuth,  dissolve  the  carbonates  -of  lead  and 
bismuth  in  dilute  nitric  acid  and  precipitate  as  BiOCl,  by 
Ledoux's  method,  thus.  Nearly  neutralize  the  nitric  acid  with 
NH4OH,  dilute  to  300  c.c.,  complete  the  neutralization,  add 
%  c.c.  HC1,  and  heat  nearly  to  boiling  for  an  hour.  Filter  on  a 
weighed  Gooch  crucible,  wash  with  hot  water,  dry  at  100°C.,  and 
weigh  as  BiOCl  containing  0.8018  bismuth. 

Notes  on  the  Process. — To  be  sure  of  the  results  it  is  necessary  to  run 
a  check  analysis  on  the  nitric  and  sulfuric  acids,  evaporating  the  same 
amount  of  them  nearly  down  to  dryness,  and  treating  the  last  of  the 
sulfuric  acid  in  the  same  way  as  the  lead  sample. 

The  results  of  refined  lead  analysis  are  apt  to  depend  more  upon  the 
chemist  than  on  the  lead,  and  it  is  desirable  that  as  many  errors  as  pos- 
sible be  eliminated  in  order  to  get  accurate  results.  One  of  the  sources 
of  error  is  in  the  chemicals  used,  which  are  not  absolutely  pure  and 
import  certain  quantities  of  iron,  copper,  arsenic  and  antimony.  The 
amount  of  nitric  and  sulfuric  acids  used  is  as  great  as  the  lead  sample, 
so  that  a  check  should  be  run  on  the  acids. 

REFERENCE : 

BETTS,  "Lead  Refining  by  Electrolysis." 

If  bismuth  alone  is  wanted,  use  the  following  method  of  Ledoux 
as  given  in  Low's  ''Technical  Methods  of  Ore  Analysis,"  page  56. 

Dissolve  25  grams  of  the  lead  in  200  c.c.  of  water  and  40  c.c.  of 
nitric  of  1.42  sp.  gr.  Warm  gently  until  all  lead  is  dissolved, 


ANALYSIS  OF  REFINED  LEAD  231 

then  add  1:2  NH4OH,  very  cautiously,  finally  drop  by  drop, 
until  the  free  acid  is  gone  and  the  liquid  remains  slightly  opales- 
cent. Now  add  1  c.c.  of  1:3  HC1.  The  solution  will  clear  for  a 
moment,  then  if  there  is  an  appreciable  amount  of  bismuth 
present  a  crystalline  precipitate  of  BiOCl  will  form.  Heat  nearly 
to  boiling  for  an  hour.  Filter  and  wash  the  precipitate  twice  with 
boiling  water.  The  precipitate  will  be  contaminated  with  some 
lead  and  antimony.  Dissolve  it  in  a  small  amount  of  hot  1:3 
HC1,  wash  the  filter  with  hot  water  and  dilute  the  filtrate  with 
water,  taking  care  that  the  dilution  is  not  so  great  as  to  cause  the 
precipitation  of  BiOCl.  Pass  H2S  through  to  precipitate  the 
lead,  bismuth  and  antimony  as  sulfides,  filter,  wash  once  with 
water,  then  with  warm  (NH4)2S  to  dissolve  the  antimony  sulfide, 
wash  again  with  water  and  dissolve  the  bismuth  and  lead  sul- 
fides by  placing  filter  and  contents  in  a  small  beaker  and  heating 
with  1:4  nitric  acid.  Boil  to  disintegrate  the  paper  and  then 
filter  and  wash  well  with  warm  dilute  nitric  acid.  Nearly  neu- 
tralize the  filtrate  with  NH4OH,  dilute  to  300  c.c.,  complete  the 
neutralization,  and  add  1  c.c.  of  1:3  hydrochloric  acid.  Keep 
hot  for  an  hour,  filter  on  a  weighed  Gooch  crucible  and  wash 
with  water,  dry  at  100°C.,  and  weigh  as  BiOCl  containing 
80.18  per  cent,  bismuth. 

Bismuth  may  be  determined  in  copper  in  the  same  way.     The 
following  is  an  analysis  of  refined  lead  in  percentages: 

Cu  Sb  Bi  Ag  Fe  Zn  Ni 


0.0004    0.0008   0.002   0.0005   0.0006   0.0008   0.0007 


CHAPTER  XXVII 
THE  ANALYSIS  OF  BEARING  METALS 

Bearing  metals  are  alloys  selected  for  bearing  linings  on  account  of 
their  combination  of  antifrictional  properties  with  sufficient  compressive 
strength  to  prevent  them  from  being  squeezed  out  of  place  under  high 
compression,  and  strength  to  avoid  breaking  under  heavy  shock. 

They  are  usually  composed  of  lead,  tin,  antimony  and  copper  in  about 
the  following  proportions:  lead  70  per  cent.,  tin  15  per  cent.,  antimony  15 
per  cent.,  copper  0  to  6  per  cent.  Journal  brasses  are  composed  of  lead 
about  15  per  cent.,  tin  about  10  per  cent,  and  copper  about  75  per  cent. 

There  are  innumerable  methods  of  analyzing  alloys  of  lead,  tin,  anti- 
mony and  copper,  but  the  following  method  has  given  the  writer  the 
best  results  with  a  moderate  expenditure  of  time. 

When  the  alloy  is  digested  with  sulfuric  acid  under  proper  condition, 
the  tin,  antimony  and  copper  all  go  in  solution  and  the  lead  remains  as 
insoluble  lead  sulfate.  In  the  filtrate  the  antimony  is  foundasSb2(S04)3, 
the  arsenic  as  As2(S04)3,  and  the  tin  and  copper  in  their  "ic"  states. 
The  arsenic  is  distilled  off  and  titrated  with  iodine,  antimony  is  titrated 
to  the  pentavalent  state  by  standard  permanganate  and  the  copper  pre- 
cipitated as  sulfocyanate  after  the  antimony  is  titrated.  Tin  is  deter- 
mined in  another  sample  in  the  filtrate  from  the  lead  sulfate  either  with 
or  without  a  previous  titration  of  the  antimony.  The  results  obtained 
are  excellent  and  the  time  and  attention  required  slight.  If  copper  is 
not  wanted,  lead,  antimony  and  tin  can  be  determined  on  the  same 
sample. 

Process  of  Analysis. — Place  1  gram  of  the  fine  drillings  or 
shavings  in  a  Kjeldahl  flask,  add  10  c.c.  of  sulfuric  acid,  sp.  gr. 
1.84,  heat  the  flask  over  a  bare  flame  and  keep  the  sulfuric  acid  at 
or  near  boiling  until  the  residue  in  the  flask  is  pure  white.  Cool, 
add  20  c.c.  of  water  all  at  once  to  the  sulfuric  acid,  boil  for  several 
minutes,  allow  the  lead  sulfate  to  settle  a  few  minutes,  cool  to 
about  50°C.,  and  pour  the  clear  liquid  through  a  weighed  Gooch 
crucible  with  an  asbestos  mat,  without  allowing  the  lead  sulfate 
to  pass  out  of  the  flask.  Put  10  c.c.  more  strong  sulfuric  acid  in 
the  flask  and  heat  at  boiling  temperature  for  15  minutes,  cool,  add 

232 


THE  ANALYHIX  OF  BEARING  METALS  233 

30  c.c.  of  water,  boil,  cool  and  filter  through  the  same  Gooch 
as  before.  Wash  all  the  lead  sulfate  out  of  the  flask  into  the 
Gooch  crucible,  wash  the  crucible  and  sulfate  five  times  with 
small  amounts  of  water,  and  carefully  ignite  the  crucible.  To  do 
this  place  the  crucible  inside  a  larger  one  and  heat  the  outside  one 
to  a  dull  red  for  10  minutes,  or,  better,  heat  in  a  dull  red  hot 
muffle.  Cool  and  weigh.  The  weight  of  the  lead  sulfate  mul- 
tiplied by  0.683  gives  the  weight  of  the  lead. 

If  arsenic  is  present  proceed  as  directed  on  page  234;  if  not, 
proceed  as  directed  below. 

Antimony. — Heat  the  filtrate,  which  should  be  less  than  150 
c.c.  in  volume,  to  60°C.  and  titrate  with  standard  permanganate 
solution.  Run  in  the  permanganate  until  the  pink  color,  which 
quickly  appears  and  does  not  fade,  becomes  a  deep  permanga- 
nate color.  Agitate  the  solution  a  minute  and  then  titrate 
the  excess  permanganate  by  standard  ferrous  sulfate  solution. 
The  KMnO4  should  be  standardized  against  pure  antimony 
treated  in  the  same  way.  The  iron  value  of  the  permanganate 
used  minus  the  iron  value  of  the  ferrous  sulfate  used  multiplied 
by  1.076  theoretically  equals  the  antimony  present.  That  is, 
a  permanganate  solution,  1  c.c.  of  which  equals  0.010  gram  of 
iron,  equals  0.01076  gram  theoretically  of  antimony.  The  end 
point  is  sharp  and  the  results  exact.  It  is  not  necessary  or 
desirable  to  have  HC1  present. 

Copper. — Now  add  3  grams  of  tartaric  acid  to  the  solution  and 
then  NH4OH  until  the  solution  is  slightly  alkaline,  then  add  2 
c.c.  of  sulfuric  acid  and  heat  almost  to  boiling.  Add  2  grams  of 
Na2SO3  and  when  all  is  dissolved  add  a  gram  of  KCNS  dissolved 
in  10  c.c.  of  water.  Shake  the  flask  well  and  allow  the  precipi- 
tate to  settle  for  15  minutes  while  the  solution  is  kept  hot. 
Filter  through  an  asbestos  mat,  wash  well  with  water  and  then 
pour  through  the  filter  40  c.c.  of  10  percent.  NaOH,  catching  the 
solution  in  a  clean  beaker  or  flask.  Wash  the  filter  well  with 
water  and  titrate  the  sulfocyanate  as  directed  on  page  211,  for 
the  analysis  of  copper  ores.  . 

Tin. — At  the  same  time  that  the  above  analyses  are  being 
made,  carry  through  another  sample  up  to  or  through  the  titra- 
tion  for  antimony,  thus  getting  checks  on  the  lead  and  antimony 
results.  Then  add  to  the  solution  one-third  its  volume  of  strong 


234  METALLURGICAL  ANALYSIS 

HC1,  transfer  the  solution  to  a  500  c.c.  flask  and  stopper  the  flask 
with  a  three-hole  stopper.  Through  one  hole  pass  a  glass 
tube  which  extends  to  the  bottom  of  the  flask.  Through  another 
pass  an  iron  rod,  the  end  in  the  flask  being  bent  into  a  coil. 
Add  to  the  solution  5  c.c.  of  sulfuric  acid  containing  0.15  gram 
'of  antimony  unless  the  sample  contains  a  sufficient  amount 
already.  Heat  to  boiling  and  pass  a  stream  of  CO2  or  natural 
gas  freed  from  H2S  by  NaOH,  through  the  solution  by  means  of 
the  glass  tube.  Continue  the  boiling  (and  current  of  gas)  for 
20  minutes  after  the  solution  becomes  colorless.  Cool  the  solu- 
tion under  a  jet  of  water  without  stopping  the  current  of  gas, 
which  should  pass  through  rapidly  while  the  flask  is  cooling  to 
prevent  the  air  from  being  drawn  in.  When  cool,  run  in  through 
the  vacant  hole  100  c.c.  of  distilled  water,  3  c.c.  of  starch  solu- 
tion, draw  up  the  iron  rod,  and  titrate  the  tin  with  a  N/10  solu- 
tion of  iodine.  The  blue  end  point  fades  after  about  a  minute. 

MODIFICATION  WHEN  ARSENIC  is  PRESENT 

If  the  metal  contains  arsenic  the  above  process  must  be  modified 
because  arsenic  interferes  with  the  determination  of  antimony. 

Process  of  Analysis. — Evaporate  the  filtrate  from  the  lead 
sulfate  until  fumes  of  sulfuric  acid  appear,  cool,  add  15  c.c.  of 
water,  35  c.c.  of  HC1,  sp.  gr.  1.20,  and  insert  in  the  flask  a,  clean 
rubber  stopper,  carrying  a  centigrade  thermometer  and  a  delivery 
tube.  The  thermometer  should  be  about  1  in.  from  the  surface 
of  the  liquid,  so  as  to  get  the  vapor  temperature  only,  which 
should  not  go  above  108°C.  Connect  the  delivery  tube  to  a 
figure  S  condenser  which  has  one  of  its  curves  nearly  filled  with 
water  and  submerged  in  cold  water  in  a  500  c.c.  beaker,  and  its 
other  free  end  dipping  into  about  75  c.c.  of  water  in  a  300  c.c. 
beaker. 

The  S  condenser  is  about  18  in.  long  and  %  in.  inside  diameter 
but  tapers  to  alpout  Y±  in.  at  the  upper,  and  J^  in.  at  the  lower  end 
to  facilitate  washing  and  to  make  the  bubbles  of  gas  small  as  they 
emerge  into  the  beaker.  This  makes  a  perfect  condensing  appara- 
tus in  this  case;  it  is  very  simple,  easy  to  handle,  has  only  one 
rubber  connection  besides  the  rubber  stopper,  and  no  cocks  or 


THE  ANALYSIS  OF  BEARING  METALS  235 

corks  that  leak.  Nothing  is  lost  through  it  except  air  from  the 
flask  at  the  very  start. 

Distill  from  10  to  15  minutes,  boiling  gently,  and  keeping  the 
vapor  temperature  at  107°  for  at  least  five  minutes.  The  arsenic, 
as  AsCl3,  is  all  distilled  over  even  if  the  alloy  contains  5  per  cent., 
which  is  rare. 

Arsenic. — Wash  out  the  condenser  into  the  300  c.c.  beaker,  and 
add  an  excess  of  about  2  grams  sodium  bicarbonate  to  this  solu- 
tion which  should  now  have  a  volume  of  about  200  c.c.,  and  warm 
to  a  temperature  of  about  27°C.  Titrate  with  standard  iodine 
solution  (page  225)  and  starch  to  a  deep  blue,  which  color  will 
take  0.2  c.c.  of  iodine  solution  in  a  blank  under  the  conditions 
used. 

Antimony. — Cool  the  solution  left  in  the  flask,  add  about  130 
c.c.  of  cold  water  and  titrate  with  standard  permanganate  solu- 
tion. The  blank  is  0.1  c.c.  About  4  c.c.  of  hydrochloric  acid 
must  be  present  during  this  titration;  usually  enough  is  left  in 
the  flask  from  the  distillation. 

Tin. — Determine  the  tin  as  directed  above. 

Notes  on  the  Process. — Arsenic  consumes  close  to  1.5  times  as  much 
permanganate  solution  as  antimony  does.  Hence,  if  the  arsenic  is  not 
removed  before  the  antimony  determination,  the  results  will  be  worth- 
less. Most  all  alloys  which  contain  antimony  contain  arsenic.  The 
arsenic  should  be  removed  before  the  tin  determination  since  it  often 
causes  high  results  in  this  case  too. 

Copper  has  no  effect  whatever  on  the  antimony  determination  but 
when  it  exceeds  about  3  per  cent,  it  is  apt  to  interfere  with  the  tin  deter- 
mination. The  amount  of  iron  found  in  alloys  is  usually  entirely  oxi- 
dized in  the  concentrated  sulfuric  acid  to  the  ferric  state  so  that  it  does 
not  interfere.  There  are  no  other  common  metals  that  interfere. 

About  the  only  causes  of  error  in  this  method  are  too  great  a  variation 
of  the  conditions  stated  and  the  use  of  impure  chemicals. 

For  the  reactions  and  remarks  for  the  copper  titration  see  page  210. 
For  those  for  the  tin  titration  see  page  219.  For  the  arsenic  titration 
see  page  174. 

When  the  alloy  containing  antimony  is  dissolved  in  strong  hot  sul- 
furic acid  the  antimony  goes  into  solution  as  Sb2(SO4)3.  This  is 
titrated  by  the  permanganate,  thus, 

5Sb2(S04)i+4KMnO4-f  24H20  = 

10H3SbO4+2K2S04+4MnS04+9H2S04. 


236  METALLURGICAL  ANALYSIS 

It  is  not  best  to  have  hydrochloric  acid  present  when  the  antimony  is 
titrated  as  the  end  point  is  so  transient. 

When  the  antimony  is  being  titrated  the  solution  will  become  pink 
long  before  the  end  point  is  reached,  in  fact  the  pink  appears  soon  after 
the  titration  is  started.  The  permanganate  must  be  added  until  the 
solution  becomes  a  deep  permanganate  color  and  the  excess  is  then 
titrated  with  ferrous  sulfate.  If  the  solution  contains  20  per  cent. 
HC1  the  pink  color  does  not  appear  before  the  end  point  is  reached  but 
the  end  color  is  evanescent. 

REFERENCES: 

DEMOREST,  J.  Ind.  Eng.  Chem.,  V,  842. 

STIEF,  J.  'Ind.  Eng.  Chem.,  VII,  211. 
REFERENCES  ON  OTHER  METHODS: 

Low,  "Technical  Methods  of  Ore  Analysis,"  p.  333. 

PRICE  and  MEAD,  "Technical  Methods  of  Brass  Analysis,"  pp.  157, 
164. 

McCAY,  J.  Am.  Chem.  Soc.,  XXXI,  373.     Separation  of  Sn  and  Sb. 

DINAM,  Mon.  Sci.,  XXII,  600. 

KIETREIBER,  OsteiT.  Chem.  Ztg.,  XIII,  146. 

GOODWIN,  J.  Ind.  Eng.  Chem.,  Ill,  34. 

KOPENHAGUE,  Ann.  chim.  Anal.,  XVII,  241. 

McCAY,  J.  Am.  Chem.  Soc.,  XXXII,  1241. 


CHAPTER  XXVIII 
THE  ANALYSIS  OF  SPELTER 

Process  of  Analysis. — Dissolve  10  grams  of  sample  in  dilute 
nitric  acid,  boil,  allow  to  settle,  filter,  wash,  dry  and  ignite  the 
precipitate  as  SnO2.  Generally  there  is  no  tin  in  the  zinc  and 
the  solution  is  not  filtered. 

Dilute  to  250  c.c.,  add  enough  nitric  acid  to  have  15  per  cent, 
present  and  electrolyze  at  a  temperature  of  50°C.  and  a  current 
of  2  amperes,  using  preferably  a  gauze  anode.  The  lead  is  all 
deposited  in  about  a  half  hour.  Dip  the  anode  quickly  in  a 
beaker  of  pure  water,  then  wash  with  alcohol,  dry  for  15  minutes 
at  230°C.  and  weigh.  The  precipitate  of  Pb02  contains  when 
dried  in  this  way  86.43  per  cent.  Pb. 

Iron. — Weigh  5  grams  of  sample  and  put  in  a  150  c.c.  flask. 
Add  20  c.c.  of  water  and  10  c.c.  of  hydrochloric  acid  and  heat. 
When  the  action  slows  down  add  30  c.c.  of  1:3  sulfuric  acid. 
When  the  zinc  is  all  dissolved  fill  the  flask  to  the  neck  with  dis- 
tilled water  and  filter  quickly  through  a  thin  paper  or  pulp. 
The  residue  on  the  paper  consists  chiefly  of  lead.  Dilute  the 
filtrate  to  400  c.c.  and  titrate  the  iron  with  permanganate  of 
about  N/20  strength. 

When  the  sample  is  dissolved  the  iron  goes  in  solution  as  fer- 
rous iron.  For  absolutely  accurate  results  the  titrated  solution 
should  be  again  reduced,  this  time  with  H2S,  the  excess  H2S 
boiled  off  while  a  current  of  CO2  passes  through,  the  solution 
cooled  and  titrated. 

Cadmium. — Dissolve  20  grams  of  the  sample  in  dilute  hydro-v 
chloric  acid  sufficient  to  dissolve  all  the  zinc  except  about  a  half 
gram.  Filter  off  the  residue  of  zinc,  lead  and  cadmium  and  wash 
two  times.  Dissolve  the  residue  in  a  little  nitric  acid,  add  1  c.c. 
of  sulfuric  acid  and  evaporate  to  fumes.  Add  20  c.c.  of  water, 
heat  to  dissolve  all  cadmium  sulfate  and  filter  off  the  lead  sulfato. 
Make  the  filtrate  alkaline  with  NH4OH  in  excess,  boil  and  filter 

237 


238  METALLURGICAL  ANALYSIS 

off  any  bismuth.  Make  the  filtrate  slightly  acid  with  sulfuric 
acid  and  precipitate  the  cadmium  with  H2S  from  the  hot  solu- 
tion. Filter  and  wash  a  few  times  with  H2S  water.  Wash  the 
precipitate  back  into  the  beaker,  add  a  little  KCN  and  shake 
until  any  copper  sulfide  is  dissolved.  Filter  and  wash  well  (on 
a  small  paper)  with  H2S  water. 

Dissolve  the  sulfide  in  hot  1 : 1  HC1  catching  the  solution  in 
a  weighed  porcelain  crucible.  Add  a  few  drops  of  sulfuric  acid 
and  evaporate  to  dryness,  finally  drive  off  the  sulfuric  acid  at  as 
low  a  heat  as  possible.  Weigh  and  multiply  the  weight  of  the 
cadmium  sulfate  by  0.5390  to  get  the  weight  of  cadmium. 

REFERENCES: 

BERRINGER,  "A  text-book  of  Assaying,"  p.  268. 
PRICE  and  MEAD,  "Technical  Brass  Analysis,"  p.  205. 
ERICSON,  Chem.  Abs.,  VI,  p.  3249. 
FAIRLIE,  Metal  Ind.,  VIII,  386. 

The  following  method  for  spelter  analysis  is  recommended  by 
Ericson  (J.  Ind.  Eng.  Chem.,  V,  401).  Dissolve  19.2  grams  of 
the  sample  in  200  c.c.  of  water  and  43  c.c.  of  concentrated  HC1, 
sp.  gr.  1.2.  Allow  to  stand  over  night,  filter  off  the  residue  of 
lead,  cadmium,  and  undissolved  zinc,  and  wash  with  hot  water. 
Transfer  the  residue  back  to  the  beaker  with  a  jet  of  water,  add 
10  c.c.  of  strong  HNO3  and  boil  until  brown  fumes  cease  to  come 
off.  Filter,  if  traces  of  antimony  or  tin  make  the  solution  turbid. 
Add  75  c.c.  of  water,  30  c.c.  of  NH4OH,  and  5  to  10  grams  of 
ammonium  persulfate.  Boil  for  five  minutes  and  let  the  PbO2 
settle  for  10  minutes.  While  still  warm,  filter  through  double 
filter  paper  and  wash  four  times  with  a  hot  10  per  cent.  NHUOH 
solution  and  then  five  times  with  hot  water.  Transfer  the  pre- 
cipitate back  into  the  beaker,  add  25  c.c.  of  hydrogen  peroxide 
solution  (20  c.c.  of  U.  S.  P.  H2O2  in  a  liter  of  water  plus  50  c.c. 
concentrated  HNO3).  Stir  until  the  PbO2  is  dissolved,  add  15 
c.c.  of  nitric  acid,  sp.  gr.  1.2,  and  100  c.c.  of  distilled  water,  and 
titrate  the  excess  of  H2O2  with  standard  permanganate,  con- 
taining 0.568  gram  of  permanganate  to  the  liter.  Then  the  per- 
manganate equal  to  the  H202  solution  used  minus  the  perman- 
ganate required  in  the  titration  equals  the  lead  in  the  sample  in 
hundredths  per  cent.  That  is,  if  the  H2O2  is  equal  to  70  c.c.,  and 


THE  ANALYSIS  OF  SPELTER  239 

30  c.c.  of  permanganate  are  used  in  the  titration,  the  lead  equals 
0.40  per  cent,  of  the  sample.     The  reactions  are 

Pb02+H202+2HN03  =  Pb(N03)2+2H20+O2 
5H202+2KMn04+6HN03  =  2KN03+2Mn(N03)2+8H20+  5O2 

Hence  2KMn04  =  5Pb  =  10Fe  and  theoretically  j         =  1.851, 


but  actually  the  ratio  is  found  to  be  1.92. 

In  the  filtrate  from  the  PbO2  the  cadmium  is  determined  as 
follows:  boil  the  solution  until  nearly  neutral  and  a  white  pre- 
cipitate forms,  take  off  the  hot  plate  and  add  40  c.c.  of  1:3  sul- 
furic  acid.  Boil  10  minutes,  dilute  to  200  c.c.  and  precipitate 
the  cadmium  with  H2S.  Filter  through  double  filter  paper  and 
wash  a  few  times.  Dissolve  the  precipitate  in  as  little  warm 
dilute  HC1  as  possible  and  wash  with  warm  water.  If  copper  is 
present  it  remains  insoluble. 

Nearly  neutralize  the  filtrate  with  NH4OH,  add  8  grams  of 
trichloracetic  acid,  dilute  to  200  c.c.  and  precipitate  the  cadmium 
with  H2S.  Filter  off  the  CdS  and  determine  it  as  above  directed. 


CHAPTER  XXIX 
BRASS  AND  BRONZE  ANALYSIS 

Brass  is  essentially  an  alloy  of  copper  and  zinc  and  bronze  an  alloy 
of  copper  and  tin,  but  brass  may  have  small  amounts  of  lead  and  tin 
and  other  elements  and  bronze  may  have  small  amounts  of  lead  and 
zinc  and  other  elements. 

Analysis  of  Brass. — Dissolve  1  gram  of  the  drillings  with  a 
mixture  of  5  c.c.  of  water  and  10  c.c.  of  nitric  acid.  Cover  with 
a  glass  and  heat  to  boiling.  When  all  red  fumes  are  gone  dilute 
to  75  c.c.  and  filter  through  a  paper  onto  which  has  been  sucked 
macerated  filter  paper  by  means  of  a  suctiori  filter  arrangement. 
Wash  well  and  if  accurate  results  are  not  desired  ignite  the  pre- 
cipitate in  a  porcelain  crucible  and  weigh  as  SnO2  containing 
78.8  per  cent.  tin.  Since  the  SnC>2  is  contaminated  with  all  the 
phosphorus  in  the  sample  and  with  more  or  less  copper  and  lead 
if  present,  it  must  be  purified  if  accurate  results  are  required. 
To  do  this,  peel  the  mat  of  macerated  paper  and  the  precipitate 
of  metastannic  acid  off  of  the  filter  paper,  put  it  in  the  beaker  in 
which  the  sample  was  dissolved  and  add  25  c.c.  of  NH4HS  made 
by  saturating  ammonia  with  H2S.  Heat  until  all  the  precipi- 
tate is  dissolved  except  the  small  amount  of  sulfides  of  copper 
and  lead,  etc.  Filter  through  the  same  paper  as  before  and  wash 
well  with  dilute  NH4HS  water  and  electrolyze  the  filtrate  after 
adding  4  grams  of  KCN  and  diluting  to  150  c.c.  Use  a  gauze 
cathode  and  a  current  of  about  3  amperes.  The  KCN  keeps  sul- 
fur from  separating  on  the  anode.  The  tin  will  all  be  deposited 
in  30  to  60  minutes.  If  the  chemist  prefers,  he  may  determine 
the  tin  in  the  precipitate  of  metastannic  acid  by  treating  it,  paper 
and  all,  exactly  as  described  for  tin  in  bearing  metals  on  page  233. 

To  the  filtrate  from  the  metastannic  acid,  to  which  is  added 
the  sulfides  obtained  from  the  treatment  of  the  metastannic  acid 
with  NH4HS,  add  5  c.c.  of  sulfuric  acid  and  evaporate  to  fumes. 
Add  50  c.c.  of  water,  heat  until  all  copper  sulfate  is  dissolved, 

240 


BRASS  AND  BRONZE  ANALYSIS  241 

cool,  filter  and  wash  the  lead  sulfate  with  cold  dilute  sulfuric 
acid.  The  filter  should  be  a  Gooch  crucible  with  asbestos  mat. 
Ignite  and  weigh  as  directed  on  page  233. 

Electrolyze  the  filtrate  from  the  lead  sulfate  for  copper  after 
adding  5  c.c.  of  HN03,  and  after  the  copper  is  all  out  determine 
iron  and  zinc  by  precipitating  the  iron  by  NH4OH  and  the  zinc 
by  Waring's  method,  as  given  on  page  196. 

If  the  sample  does  not  contain  tin,  the  solution  is  evaporated 
with  sulfuric  acid  to  fumes  and  the  analysis  carried  on  as  given 
above  after  the  evaporation  with  sulfuric  acid. 

If  the  brass  does  not  contain  tin  and  not  much  manganese, 
dissolve  1  gram  in  20  c.c.  of  nitric  acid,  and  dilute  to  100  c.c. 
and  electrolyze  (using  gauze  cathode  and  anode)  until  the  lead 
is  deposited  as  PbO2,  then  add  10  c.c.  of  NH4OH  and  complete 
the  deposition  of  the  copper. 

Solder  Analysis. — Solders  are  composed  of  about  half  and  half 
lead  and  tin  and  may  be  correctly  analyzed  either  as  directed 
above  for  brass,  or,  even  better,  as  directed  for  the  analysis  of 
bearing  metals. 

Bronze  Analysis. — Bronzes  should  be  analyzed  as  directed  for 
the  analysis  of  brass,  always  dissolving  the  metastannic  acid  in 
NH4HS  and  precipitating  the  tin  electrolytically.  The  metas- 
tannic acid  may  be  treated  as  directed  under  bearing  metal 
analysis  for  tin. 

REFERENCES: 

DEMOREST,  J.  Ind.  Eng.  Chem.,  March,  1910. 

PRICE  and  MEAD,  "Technical  Analysis  of  Brass,"  p.  180. 


10 


CHAPTER  XXX 
THE  ANALYSIS  OF  COAL  AND  COKE 

In  the  laboratory  examination  of  coal  the  points  to  be  investigated  are 
usually:  First,  the  amount  of  moisture  that  it  contains  as  it  occurs  in 
the  mine  or  on  the  market.  Second,  the  amount  of  the  impurities 
present  that  affect  its  use,  such  as  ash,  sulfur,  and  phosphorus.  Third, 
the  amount  and  quality  of  the  coke  that  it  will  produce.  Fourth,  the 
improvement  that  it  undergoes  by  "  washing."  Fifth,  the  fuel  value,  in- 
cluding the  calorific  power  and  the  evaporating  power. 

The  sampling  of  coal  is  always  a  matter  of  considerable  difficulty,  as  it 
deals  with  a  mechanical  mixture  of  several  minerals  which  differ  greatly 
in  specific  gravity;  namely,  pure  coal,  slate,  bone  coal  and  iron  pyrite. 
These  constituent  minerals  may  occur  in  all  degrees  of  size ;  for  instance, 
the  pyrite  may  be  present  as  barely  visible  grains  scattered  all  through 
the  coal  or  as  large  lumps  and  streaks.  It  is  obvious  that  in  the  latter 
case  the  difficulty  of  securing  a  small  sample  which  shall  contain  the 
same  percentage  of  the  heavy  pyrite  as  does  the  mass  from  which  it  is 
drawn  is  formidable.  See  page  6. 

Finely  crushed  coal  is  liable  to  oxidation  and  change  of  composition  on 
standing  exposed  to  air  at  ordinary  temperatures.  Hence  the  analysis 
should  be  made  soon  after  the  final  sampling. 

The  laboratory  processes  in  use  for  coal  testing  comprise  the  "proxi- 
mate" analysis,  the  ultimate  analysis,  the  determination  of  sulfur  and 
phosphorus,  tests  of  the  coking  power,  washing  the  coal,  and  finally  the 
determination  of  the  heating  power  either  by  calculation  from  the  re- 
sults of  the  ultimate  analysis,  or  by  use  of  the  calorimeter. 

PROXIMATE  ANALYSIS 

The  method  for  proximate  analysis  here  used  is  as  given  by  Professor 
E.  E.  Somermeier  of  the  Department  of  Metallurgy,  Ohio  State  Univer- 
sity, in  his  book,  "Coal." 

This  analysis  gives  the  composition  of  the  coal  under  four  headings  as 
follows:  moisture,  volatile  matter,  fixed  carbon,  and  ash. 

The  results  obtained  are  more  or  less  dependent  upon  the  exact  process 
used  and  small  variations  in  working  out  the  details  of  the  process  may 

242 


THE  ANALYSIS  OF  COAL  AND  COKE  243 

make  a  considerable  difference  in  the  results  actually  obtained,  while  a 
distinctly  different  process  gives  radically  different  values  for  some  of  the 
determinations.  Hence  the  results  are  relative  and  not  absolute  and 
should  be  so  regarded  both  by  the  chemist  and  by  the  user  of  the  coal. 
The  efforts  of  some  chemists  to  find  a  method  of  determining  the  "true 
moisture"  in  coal  might  better  be  spent  in  trying  to  simplify  and  improve 
the  method  already  in  use  for  obtaining  the  comparative  value. 

Moisture. — The  term  moisture  includes  only  the  more  or  less  loosely 
held  water  which  is  driven  off  by  heating  1  gram  of  'the  finely  ground 
sample  for  one  hour  at  105°C.  A  finely  ground  sample  of  coal  during 
the  operation  undergoes  changes  due  to  oxidation  and  escape  of  gases, 
hence  the  actual  value  obtained  for  moisture  is  the  amount  of  water 
driven  off  plus  or  minus  any  oxidation  changes.  In  most  coals  if  not 
ground  excessively  fine  these  oxidation  changes  are  of  minor  importance 
compared  to  the  moisture  loss  so  that  the  reporting  of  this  net  loss  as 
moisture  does  not  lead  to  any  serious  errors,  although  it  practically 
never  represents  the  exact  amount  of  water  expelled.  A  sample  of  coal 
which  has  been  heated  for  one  hour  at  105°  will  give  off  more  moisture 
and  undergo  further  oxidation  changes  if  heated  to  a  still  higher  tem- 
perature, the  amount  of  moisture  given  off  depending  upon  the  kind  of 
coal  and  upon  the  increase  in  temperature.  The  extent  of  the  oxidation 
also  increases  with  the  temperature  and  varies  with  the  kind  of  coal  and 
fineness  of  the  sample.  While  it  is  true  that  the  results  for  moisture 
obtained  by  heating  'the  sample  to  105°  have  no  absolute  value  but 
merely  a  relative  one,  it  is  equally  true  that  when  two  samples  of  approxi- 
mately the  same  kind  of  coal  are  treated  in  the  same  way  for  moisture 
by  heating  to  105°,  the  difference  in  the  results  obtained  show  very  closely 
the  difference  in  the  amount  of  loosely  held  moisture  in  the  coal. 
Usually  this  is  what  the  user  of  the  coal  wishes  to  know  and  on  this 
account  the  moisture  determination  has  importance  and  value. 

Volatile  Matter. — The  determination  of  volatile  matter  is  an  arbi- 
trary one  and  the  results  are  obtained  by  following  a  certain  prescribed 
procedure,  which  is  essentially  to  heat  1  gram  of  the  finely  ground  sample 
in  a  covered  platinum  crucible  over  the  full  flame  of  a  Bunsen  burner 
for  seven  minutes.  The  loss  in  weight  represents  moisture  plus  volatile 
matter.  Subtracting  the  value  for  moisture  from  this  result  gives  the 
amount  of  volatile  matter  in  the  coal. 

This  determination  cannot  be  regarded  as  entirely  satisfactory  as  the 
result  obtained  is  to  a  considerable  degree  dependent  upon  the  particu- 
lar conditions  under  which  the  sample  was  run  and  two  different  chem- 
ists in  two  different  laboratories  both  trying  to  follow  out  the  same 
method  of  procedure  may  easily  obtain  results  for  volatile  matter  upon 
the  same  sample  of  coal  which  may  differ  by  2  or  3  per  cent.  Further- 


244  METALLURGICAL  ANALYSIS 

more,  some  high-moisture  coals  suffer  mechanical  losses  during  the 
heating  to  drive  off  the  volatile  matter.  Such  samples  require  special 
treatment  to  insure  results  of  even  approximate  accuracy.  On  account 
of  such  possible  differences  and  errors  this  determination  cannot  be 
regarded  as  very  exact.  It  is,  however,  true  that  the  same  chemist 
working  in  the  same  way  with  the  same  crucibles,  the  same  height 
of  gas  flame,  the  same  Bunsen  burner,  etc.,  can  obtain  results  which 
will  duplicate  within  a  few  tenths  of  1  per  cent,  and  in  control  work 
the  same  chemist's  results  on  approximately  the  same  coals  ought 
to  be  comparable  among  themselves  to  within  less  than  1  per  cent. 
The  amount  of  volatile  matter  in  itself  gives  very  little  idea  of  the  coal, 
as  two  coals  with  approximately  the  same  amount  of  volatile  matter 
may  differ  very  greatly  in  heating  value,  physical  properties,  etc.,  and 
any  significance  which-  the  determination  of  volatile  matter  actually 
has  is  largely  a  relative  one  which  may  be  of  value  when  the  same  or 
similar  coals  are  compared  with  one  another. 

The  volatile  matter  consists  essentially  of  any  combined  water  in  the 
coal  plus  a  portion  of  the  sulfur,  on  an  average  probably  about  one- 
half  of  the  total  sulfur  present  in  the  coal,  plus  the  nitrogen  in  the 
coal,  plus  hydrocarbons  of  unknown  and  varying  composition.  The 
nitrogen  and  combined  water  in  the  volatile  matter  have  no  heating 
value  and,  if  present  in  large  amounts,  the  heating  value  of  the  com- 
bustible will  be  correspondingly  lower. 

Fixed  Carbon. — Fixed  carbon  represents  the  difference  obtained  by 
subtracting  the  percentage  of  moisture,  volatile  matter  and  ash  from 
100.  The  fixed  carbon  as  its  name  indicates  is  mostly  carbon.  Ap- 
proximately one-half  the  sulfur  in  the  coal  present  in  the  form  of  pyrite 
and  a  variable  portion  of  that  present  as  organic  sulfur  remains  with 
the  fixed  carbon  and  the  heating  value  of  the  fixed  carbon  is,  on  this 
account,  somewhat  lower  than  that  of  pure  carbon.  On  the  other 
hand,  small  amounts  of  hydrogen  may  be  retained  in  the  fixed  carbon 
which  would  slightly  increase  its  heating  value.  In  most  coals  the 
heating  value  per  unit  of  the  fixed  carbon  is  not  far  from  that  of  carbon 
— 8080  calories — and  this  value  may  be  used  in  estimating  heat  values 
without  any  great  error.  With  high  sulfur  coals,  a  somewhat  lower 
value,  approximately  30  calories  lower  for  each  per  cent,  of  sulfur  in  the 
coal,  is  probably  more  nearly  a  correct  value.  This  is  based  on  the 
assumption  that  one-half  of  the  sulfur  remains  with  the  fixed  carbon  and 
that  not  more  than  traces  of  hydrogen  are  retained  in  the  fixed  carbon. 

Ash. — As  ordinarily  reported,  this  is  the  weight  of  ignited  mineral 
matter  in  the  coal.  It  is  not  the  same  as  the  inorganic  mineral  matter 
of  the  coal,  for  clay  loses  water  on  heating,  sulfides  are  oxidized  and 
carbonates  are  calcined. 


THE  ANALYXIK  OF  COAL  AND  COKE  245 

METHODS  OF  ANALYSIS 

The  samples  from  the  sampling  room  or  laboratory  should  be 
sent  to  the  chemical  laboratory  in  wide-mouth  bottles  securely 
closed  with  rubber  stoppers.  Ordinary  4  oz.  wide-mouth  bot- 
tles are  very  convenient  for  coal  samples. 

Weighing  Out  a  Sample  for  a  Determination. — In  weighing 
out  portions  of  the  laboratory  sample  for  a  determination,  the 
sample  should  be  well  mixed.  An  efficient  method  of  mixing  is 
as  follows:  The  material  is  thoroughly  mixed  by  giving  the 
bottle  15  to  20  rotations  with  an  up-ending  and  tilting  movement 
of  the  bottle  to  insure  mixing  of  the  top  and  bottom  portions  of 
the  sample.  For  satisfactory  mixing  in  this  way  the  sample 
should  not  fill  the  bottle  more  than  half  full.  After  the  mixing 
in  the  bottle  the  stopper  is  removed  and  the  sample  still  further 
mixed  by  means  of  a  sampling  spoon,  and  successive  small  por- 
tions taken  until  the  amount  required  for  the  determination  is 
secured,  especial  care  being  taken  to  again  securely  stopper  the 
bottle  before  setting  it  aside  for  other  determinations.  If  the 
sample  more  than  half  fills  the  bottle  it  should  be  emptied  out 
on  paper,  well  mixed  and  a  sufficient  amount  discarded  until 
the  remainder  is  small  enough  to  be  properly  handled  in  the 
sampling  bottle. 

Moisture. — A  1  gram  portion  of  the  well-mixed  60-mesh 
sample  is  weighed  into  an  empty  capsule  or  crucible  and  heated 
for  an  hour  at  105°C.  in  a  constant-temperature  oven.  The  cap- 
sule is  then  removed  from  the  oven,  covered  and  cooled  in  a 
desiccator  over  sulfuric  acid. 

The  loss  in  weight  times  100  is  considered  as  the  percentage  of  mois- 
ture. The  writer  prefers,  for  moisture  determinations,  porcelain 
capsules  about  1  in.  high  by  1%  in.  in  diameter  at  the  top.  The 
particular  kind  used  has  been  obtained  from  The  Henry  Heil  Chemical 
Co.,  of  St.  Louis,  and  are  designated  as  porcelain  moisture-capsules 
No.  2.  They  are  much  more  substantial  and  satisfactory  than  the 
ordinary  porcelain  crucible. 

The  lids  used  in  connection  with  the  capsules  are  stamped  from  sheet 
aluminium.  They  are  light  and  unbreakable  and  much  more  convenient 
to  handle  than  the  ordinary  covers  used  with  porcelain  crucibles.  In 
weighing  out  the  sample  at  the  beginning  of  the  determination  the  lid 


246  METALLURGICAL  ANALYSIS 

is  placed  upon  the  balance  pan  under  the  empty  capsule  in  which  the 
sample  is  weighed. 

The  oven  used  for  a  number  of  years  in  this  laboratory  is  a  double- 
walled  copper  cylinder,  see  Fig.  14;  the  space  between  the  outer  and 
inner  walls  being  filled  with  a  solution  of  glycerine  in  water,  the  pro- 
portions being  so  adjusted  that  the  boiling  solution  maintains  a  tem- 
perature of  105°C.  in  the  inner  chamber  of  the  oven.  The  inner  cylinder 
is  4^  in.  in  diameter  by  .7  in.  long.  A  removable  perforated  shelf 
fits  into  this  inner  cylinder,  the  perforations  holding  six  capsules. 


FIG.  14. 

The  outer  cylinder  is  6^  in.  in  diameter  by  8  in.  long.  Concentration 
of  the  solution  is  prevented  by  means  of  a  condenser  fitted  onto  the  top 
of  the  outer  cylinder.  Air  is  admitted  into  the  inner  chamber  of  the 
oven  through  a  coil  of  block  tin  or  copper  tubing,  which  passes  around 
the  inner  cylinder  and  is  surrounded  by  the  glycerine  solution.  The 
inner  end  of  this  tubing  is  soldered  into  the  rear  wall  of  the  inner  cham- 
ber; the  outer  end  is  connected  to  a  flask  containing  concentrated 
sulfuric  acid.  During  a  determination  a  current  of  air  dried  by  passing 
through  the  sulfuric  acid  is  passed  through  the  copper  or  tin  tube  into 


THE  ANALYSIS  OF  COAL  AND  COKE  247 

the  inner  chamber  of  the  oven.  Passing  over  the  samples  it  takes  up 
the  moisture  and  escapes  through  a  small  opening  in  the  top  of  the  door 
of  the  oven.  The  air  is  passed  through  at  such  a  rate  that  a  volume 
equal  to  the  capacity  of  the  oven  passes  through  every  six  or  eight 
minutes.  Operating  a  moisture  oven  in  this  way  insures  a  uniform 
condition  in  the  oven  irrespective  of  laboratory  humidity  and  tempera- 
ture conditions,  and  results  run  at  different  times  are  strictly  comparable, 
which  is  not  the  case  in  an  ordinary  moisture  oven. 

The  cut  shows  nine  turns  of  tubing ;  however,  four  or  five  turns  are 
probably  just  as  efficient  and  are  less  expensive. 

The  use  of  sulfuric  acid  in  the  desiccator  in  which  the  moisture 
sample  is  cooled  gives  more  concordant  results  than  where  calcium 
chloride  is  used.  Experiments  show  that  if  the  dry  sample  is  allowed 
to  remain  over  calcium  chloride  for  any  considerable  period  of  time 
it  increases  in  weight  and  the  results  for  moisture  are  accordingly  low. 
To  avoid  the  danger  of  sulfuric  acid,  in  the  desiccator,  splashing  up  on 
the  bottom  of  the  capsule  when  the  desiccator  is  carried  around  the 
laboratory,  a  thin  sheet  of  asbestos  paper  should  be  placed  below  the 
capsule,  care  being  taken  to  have  it  fit  loosely  enough  in  the  desiccator 
to  allow  free  circulation  of  air. 

Ash. — The  ash  is  determined  in  the  residue  of  coal  from  the 
moisture  determination.  The  capsule  containing  the  coal  is 
placed  in  a  muffle  furnace  and  slowly  heated  until  the  volatile 
matter  is  given  off.  This  slow  heating  avoids  coking  the  sample 
and  renders  it  easier  to  burn  to  ash.  After  the  volatile  matter, 
is  expelled,  the  temperature  of  the  muffle  is  raised  to  redness  and 
the  heating  is  continued  until  all  black  carbon  is  burned  out. 
The  capsule  is  then  removed  from  the  muffle  furnace,  cooled  in  a 
desiccator  and  weighed.  It  is  then  replaced  in  the  muffle,  for 
30  minutes,  again  cooled  and  re-weighed.  If  the  change  in  weight 
is  less  than  0.0005  gram  the  ash  is  considered  burned  to  constant 
weight.  If  the  variation  is  greater  than  this,  the  ash  is  again 
ignited  for  30  minutes  and  again  cooled  and  re-weighed,  the 
process  being  continued  until  the  difference  in  weight  between 
two  successive  ignitions  is  less  than  0.0005  gram.  In  the  case  of 
coals  high  in  iron,  ignition  to  constant  weight  is  sometimes  diffi- 
cult on  account  of  small  variations  in  weight  due  to  oxidation 
and  reduction  of  the  compounds  of  iron.  The  amount  of 
ash  as  determined  represents  the  ignited  mineral  matter  in  the 
coal. 


248  METALLURGICAL  ANALYSIS 

In  regular  routine  work  the  cooling  in  desiccators  may  be  dispensed 
with  and  the  capsules  cooled  on  clay  triangles  in  the  open  air.  A  set 
of  six  triangles  mounted  on  a  wood  base  is  very  convenient  for  carrying 
the  capsules  from  the  furnace  to  the  balance  and  from  the  balance 
back  to  the  furnace.  This  arrangement  is  lighter  and  easier  to  handle 
than  desiccators  and  the  time  required  for  cooling  is  much  less. 

The  capsules  cooled  in  air  weigh  about  0.0005  gram  more  than  if 
cooled  in  desiccators,  hence  the  ash  results  run  a  trifle  high,  but  for 
most  samples  the  difference  is  of  very  minor  importance  and  the  saving 
in  time  and  labor  considerable.  If  results  of  highest  accuracy  are 
required  the  cooling  should  be  done  in  desiccators. 

Volatile  Matter — A  1-gram  sample  of  the  fine  (60-mesh)  coal 
is  weighed  into  a  bright,  well-burnished  20-gram  platinum  cru- 
cible with  a  close-fitting  cover.  The  crucible  and  contents  are 
heated  upon  a  platinum  or  nichrome  triangle  for  seven  minutes 
over  a  Meker  flame  not  less  than  15  cm.  high. 

The  crucible  and  residue  are  cooled  and  weighed,  the  loss  in 
weight  minus  the  weight  of  the  moisture  in  the  sample  deter- 
mined at  105°C.,  times  100  equals  the  percentage  of  volatile 
matter. 

To  protect  the  crucible  from  air  currents  it  is  desirable  to  en- 
close the  flame  in  a  chimney.  A  cylindrical  chimney  15  cm. 
long  by  7  cm.  in  diameter,  notched  at  the  top  so  that  the  platinum 
triangle  is  about  3  cm.  below  the  top  of  the  chimney,  makes  a 
satisfactory  working  arrangement. 

This  chimney  is  preferably  of  sheet-iron  lined  with  asbestos  but  a 
fairly  satisfactory  chimney  can  be  made  by  moistening  a  thick  sheet  of 
asbestos  and  rolling  it  into  a  cylinder.  This,  if  well  wrapped  with 
wire,  makes  a  fairly  serviceable  chimney.  For  lignites  and  coals 
containing  a  high  percentage  of  moisture,  the  method  should  be  modified 
by  giving  the  sample  a  preliminary  heating  at  a  low  temperature  for 
several  minutes  to  drive  out  the  moisture,  in  order  to  avoid  mechanical 
losses  which  will  occur  if  such  a  sample  is  heated  over  the  full  flame 
of  the  burner  from  the  beginning.  This  preliminary  heating  for  three 
to  four  minutes  should  be  followed  by  the  regular  seven-minute  applica- 
tion of  the  full  flame,  after  which  the  sample  is  cooled  and  weighed  as 
in  the  regular  determination. 

The  higher  the  temperature  at  which  the  volatile  matter  is  expelled 
the  greater  is  the  percentage  of  volatile  matter  obtained.  The  latest 


THE  ANALYSIS  OF  COAL  AND  COKE  249 

data  on  this  subject  (Sept.,  1912)  is  by  Fiejdner  and  Hall.1  As  a 
result  of  their  experiments  they  recommend  1000°C.  as  the  most  de- 
sirable temperature  at  which  to  make  this  determination.  Their 
results  using  a  No.  4  Meker  burner  with  natural  gas  compare  very 
favorably  with  their  results  obtained  by  heating  the  sample  in  an  elec- 
tric furnace.  The  crucible  should  be  at  least  hot  enough  to  melt  pure 
K2Cr04  (melting-point  940°C.). 

Fixed  Carbon. — The  fixed  carbon  is  the  difference  between  100  and 
the  sum  of  the  moisture,  ash  and  volatile  matter. 

The  Determination  of  Sulfur  in  Coal.  Eschka's  Method.— Sulfur 
exists  in  coal  in  three  forms:  Pyrite,  "organic  sulfur,"  and  sulfates. 
By  heating  coal  with  a  mixture  of  MgO  and  Na2COs,  and  with  ample 
access  of  air,  all  unoxidized  sulfur  is  converted  to  sulfites  and  sulfates  of 
soda  and  magnesia.  On  boiling  the  burned  mass  with  water,  these,  as 
well  as  any  sulfuric  acid  existing  previously  in  the  coal  as  sulfate,  are 
all  dissolved  out  as  alkaline  salts.  By  adding  bromine  water  to  the 
solution  the  sulfites  are  oxidized  to  sulfates,  and  then  the  total  sulfur 
can  be  estimated  as  BaS04,  by  precipitation  with  BaCl2. 

Preparation  of  the  Soda-magnesia  Mixture  (Eschka  Mixture). — 
Procure  a  "light"  calcined  magnesium  oxide,  which  must  be  free 
from  sulfur  and  water.  If  it  contains  moisture,  ignite  it  at  a  dull  red 
heat  in  a  covered  platinum  crucible.  The  heavy  dense  oxide  is  not 
satisfactory. 

Mix  two  parts  of  the  MgO  with  one  part  by  weight  of  pure  Na2C03 
previously  dried  at  a  dull-red  heat.  Grind  the  two  together  until  thor- 
oughly mixed,  and  keep  the  mixture  in  a  glass-stoppered  bottle. 

If  a  satisfactory  sample  of  sulfur-free  MgO  is  not  available,  it  may  be 
prepared  as  follows : 

Take  a  good  quality  of  commercial  "light  calcined  magnesia;"  add 
about  2  per  cent,  of  c.p.  sodium  carbonate,  and  then  stir  it  up  in  enough 
boiling  water  to  make  a  thin  liquid.  Boil  the  mixture  a  few 
minutes  and  let  settle;  decant  off  the  liquid  by  a  siphon.  Add  water, 
stir  up,  settle,  and  again  decant.  Continue  this  washing  by  decanta- 
tion  until  a  portion  of  the  liquid,  after  being  acidified  with  HC1,  shows 
no  trace  of  sulfates  when  tested  with  BaCl2.  Now  pour  the  MgO 
onto  a  large  filter,  let  it  drain  and  air  dry.  It  is  now  free  from  sulfur 
compounds.  Ignite  the  air  dried  MgO  in  a  covered  platinum  crucible 
until  all  water  is  expelled. 

A  clean  tin  bucket  can  be  used  in  this  process  where  a  quantity  is  to 
be  prepared. 

1  Eighth  International  Congress  of  Applied  Chemistry,  X,  p.  139. 


250  METALLURGICAL  ANALYSIS 

Process  of  Analysis. — Weigh  1  gram  of  the  coal  or  coke  (which 
must  be  finely  powdered,  especially  in  the  "case  of  coke),  then 
weigh  or  measure  out  roughly  2  grams  of  the  "Eschka  mixture." 
Put  about  two-thirds  of  this  into  a  30  c.c.  platinum  crucible. 
Add  the  weighed  coal  and  stir  the  mixture  in  the  crucible  thor- 
oughly with  a  small  platinum  spatula  or  glass  rod,  and  then  settle 
it  down  by  tapping  the  crucible  on  the  table.  Now  cover  the 
contents  of  the  crucible  with  the  remaining  portion  of  the 
"Eschka  mixture."  Set  the  crucible,  in  an  inclined  position, 
over  a  small  alcohol  or  sulfur-free  natural-gas  flame,  so  that  the 
tip  of  the  flame  may  barely  touch  the  crucible  near  the  top  of  the 
mixture.  The  heat  must  be  carefully  regulated,  so  that  no 
blackening  of  the  white  cover  layer  takes  place,  and  no  trace  of 
smoke  appears.  The  cover  should  be  laid  against  the  mouth  of 
the  crucible  to  assist  the  draught.  The  mixture  soon  ignites 
and  will  gradually  burn  through,  as  may  be  observed  through 
fissures  which  open  in  the  mass.  The  coal  will  usually  burn 
completely  in  less  than  an  hour.  The  heat  may  be  raised  toward 
the  end  of  the  combustion  and  the  lamp  set  back  under  the  bot- 
tom of  the  crucible.  A  higher  heat  may  be  used  with  cokes 
from  the  start;  as  these  give  no  volatile  products  and  burn 
slowly.  Stir  up  the  powder  occasionally  with  a  hot  glass  rod  or 
platinum  wire.  When  the  burning  is  complete,  all  trace  of  the 
black  coal  will  have  disappeared  and  only  a  light,  reddish-gray 
mass  remain.  Cool  and  then  pour  the  powder  into'  a  200  c.c. 
beaker.  Add  about  75  c.c.  of  boiling  water,  stir  and  digest  on 
a  water-bath.  Then  filter,  washing  the  residue  twice  by  adding 
about  30  c.c.  of  hot  water,  and  decanting  off,  then  transfer  to 
the  filter.  Wash  on  the  filter  until  the  volume  of  the  filtrate 
amounts  to  about  200  c.c.  This  will  extract  practically  all  of 
the  sulfur. 

Add  bromine  water  to  the  filtrate  until  the  liquid  is  colored 
yellow;  then  add  3  c.c.  of  HC1  and  warm  until  the  C02  is  ex- 
pelled. Test  the  solution  with  litmus  paper  to  make  sure  that  it 
is  distinctly  acid.  Then  add  10  c.c.  of  BaCl2  solution  (10  per 
cent.).  Set  the  beaker  on  a  warm  plate,  but  do  not  let  it  come 
to  boiling.  Stir  the  liquid  occasionally  until  the  BaSO4  becomes 
granular  and  settles  well.  Now  filter,  wash,  dry,  ignite  and 
weigh  the  BaS04.  Calculate  the  sulfur  as  S. 


THE  ANALYSIS  OF  COAL  AND  COKE  251 

Always  examine  the  residue  which  was  extracted  with  water, 
by  washing  it  off  the  filter  into  a  beaker,  and  then  adding  a  little 
HC1  and  warming.  All  will  dissolve  but  a  little  ash.  If  more 
than  a  trace  of  unburned  coal  is  seen  in  the  residue,  the  analysis 
must  be  repeated. 

The  residue  sometimes  retains  a  very  small  trace  of  sulfur. 
To  test  it,  add  a  little  bromine  water  with  the  HC1  as  above  and 
boil.  Filter  off  the  liquid  and  add  BaCl2.  If  any  sulfur  is 
found,  add  it  to  the  main  precipitate. 

Notes  on  the  Process. — This  is  one  of  the  best  methods  for  the  deter- 
mination of  sulfur  in  coals.  If  care  be  taken  in  all  details,  especially  as 
to  rate  of  heating,  there  is  no  loss  of  sulfur  whatever. 

It  has  been  proposed  to  substitute  K2C03  for  the  Na2C03,  the  claim 
being  made  that  there  is  less  danger  of  loss  of  S  with  the  potassium 
carbonate,  but  experience  has  shown  it  to  be  absolutely  unnecessary. 

The  use  of  alcohol  or  sulfur-free  natural  gas  as  a  source  of  heat  is 
essential.  All  coal  gas  contains  sufficient  sulfur  to  vitiate  the  results. 

The  most  difficult  step  in  the  process  is  the  burning  out.  In  analyzing 
coke  much  time  can  be  saved  by  using  a  higher  heat  than  is  given  by  an 
alcohol  lamp.  This  can  be  obtained  by  using  a  gasoline  blast  lamp  or 
working  in  a  muffle  heated  by  gasoline.  If  the  muffle  is  heated  by  coke 
or  coal  gas,  care  must  be  taken  that  no  sulfur  gets  into  it  from  the  fuej. 

Determinations  of  ash  in  coal  and  coke  must  not  be  made  in  the  muffle 
at  the  same  time  with  sulfur  determinations;  as  the  862  formed  will  be 
absorbed  by  the  "Eschka  mixture"  and  makes  the  results  high. 

Cokes  can  be  burned  with  "Eschka  mixture"  in  a  platinum  dish. 
They  should  be  stirred  frequently,  which  will  hasten  the  combustion. 
It  is  unsafe  to  treat  coals  high  in.  volatile  matter  in  this  way;  because 
the  gas  given  off  must  be  burned  in  the  mixture  and  not  on  the  surface, 
or  sulfur  may  escape.  They  must  be  burned  in  the  crucible,  and  by 
properly  regulating  the  air  supply  and  the  temperature  the  gas  can  be 
rapidly  burned  as  it  is  given  off.  When  the  volatile  matter  is  expelled 
the  heat  can  be  raised  and  the  mixture  stirred. 

A  blank  determination  must  be  run  on  the  reagents. 

Sulfur  in  the  Calorimeter  Washings. — The  determination  of 
the  sulfur  in  the  washings  from  the  calorimeter  is  as  follows :  The 
washings  are  slightly  acidulated  with  hydrochloric  acid  and  fil- 
tered from  the  residue  of  ash,  the  nitrate  is  heated  to  boiling  and 
the  sulfur  precipitated  as  in  the  Eschka  method. 


252  METALLURGICAL  ANALYSIS 

REFERENCES: 

ESCHKA,  Z.  Anal.  Chem.,  XIII,  p.  344. 

DROWN,  Trans.  Am.  Inst.  Mining  Engrs.,  IX,  p.  660. 

The  Determination  of  Phosphorus  in  Coal  and  Coke. — Ten 

grams  of  the  coal  are  carefully  burned  to  ash  in  a  porcelain  cru- 
cible. The  ash  is  then  analyzed  for  phosphorus  exactly  as 
though  it  were  an  iron  ore,  excepting  that  it  is  always  necessary 
to  fuse  the  insoluble  portion.  HC1  will  not  dissolve  all  the  phos- 
phorus out  of  the  ash  even  on  prolonged  boiling,  though  the 
amount  left  is  usually  very  trifling. 

Process  of  Analysis. — Mix  the  ash  from  10  grams  of  the  coal 
with  six  times  its  weight  of  pure  Na2CO3  and  half  its  weight  of 
NaN03.  Fuse  the  mixture  in  a  platinum  crucible,  soften  the 
fusion  with  water,  dissolve  in  an  excess  of  HC1,  evaporate  to 
dryness,  take  up  with  HC1  and  water,  and  filter  from  the  SiO2; 
then  proceed  as  by  the  yellow  precipitate  method  for  phosphorus 
in  iron  ores  (page  45  et  seq.). 

The  fusion  can  be  avoided  by  the  use  of  hydrofluoric  acid  as 
follows:  Add  5  c.c.  of  dilute  HC1  and  10  c.c.  of  HF  to  the  ash  in 
the  platinum  crucible.  Evaporate  to  dryness  in  a  good  hood; 
do  not  bake  the  residue  and  thus  render  it  insoluble.  When 
cool,  add  15  c.c.  of  dilute  HC1  and  heat.  The  residue  should 
dissolve  completely,  but  a  little  insoluble  matter  may  be  filtered 
off  and  neglected.  Put  the  solution  into  a  flask,  add  NH4OH, 
then  HN03,  then  molybdic  acid  solution,  and  " shake  down" 
the  phosphorus  as  in  the  Emmerton  method.  The  yellow  pre- 
cipitate may  be  either  weighed  or  titrated. 

REFERENCE: 

See  J.  M.  CAMP,  Iron  Age,  LXV,  p.   17.     Also  ''Methods  around 
Pittsburgh,"  p.  139. 

THE  ULTIMATE  ANALYSIS  OF  COAL 

The  Determination  of  the  Carbon  and  Hydrogen  by  Combustion  in 
Oxygen. — The  coal,  placed  in  a  boat  of  porcelain  or  platinum,  is  burned 
in  a  combustion  tube,  through  which  a  current  of  purified  air  and 
oxygen  gas  is  passed.  The  H20  and  CO 2  produced  are  absorbed  and 
weighed.  As  the  coal  contains  sulfur,  the  gases  produced  by  the  com- 
bustion must  be  passed  over  lead  chromate  to  absorb  the  SO 2  formed. 

The  same  chromate  can  be  used  for  many  determinations.  As  long 
as  it  does  not  turn  green  for  more  than  one-fifth  of  the  length  in  the 


THE  ANALYSIS  OF  COAL  AND  COKE  253 

tube  it  is  perfectly  safe.  The  writer  has  used  the  same  chromate  for 
over  fifty  combustions,  and  then  tested  it  by  burning  sulfur  in  the  tube, 
and  found  no  S02  escaping  the  chromate. 

The  principal  difficulty  in  the  process  arises  from  the  fact  that  coal 
begins  to  decompose  at  a  low  temperature,  giving  off  among  other  prod- 
ucts methane,  a  gas  which  it  is  very  difficult  to  burn  completely,  and 
which  is  very  likely  to  escape  from  the  combustion  tube  unoxidized. 
To  secure  its  complete  combustion  a  long  and  hot  layer  of  copper  oxide 
is  necessary. 

The  process  requires  close  attention  to  details  and  skill  in  fitting  up 
and  manipulating  apparatus.  The  precautions  mentioned  under  the 
combustion  method  for  carbon  apply  equally  here,  especially  as  to  the 
purity  of  the  oxygen  and  the  copper  oxide.  The  latter  should  be 
examined  for  CaC03  or  other  carbonates  which  are  liable  to  give  up 
CO2  on  heating,  and  also  for  bases  which  may  absorb  C02.  CaC03 
will  be  decomposed  at  one  temperature,  and  the  CaO  formed  will 
absorb  C02  at  another.  CuO  can  be  examined  for  CaO  by  extracting 
it  with  a  little  dilute  HN03,  adding  NH4OH  in  excess,  and  then  testing 
the  liquid  with  (NH)4C204.  The  "  wire "  oxide  is  the  best  and  should  be 
used. 

The  asbestos  used  in  the  tube  must  be  freed  from  carbonates  by 
treatment  with  HC1  and  ignition. 

The  oxygen  must  be  tested  as  to  its  purity,  and  must  not  be  kept 
in  rubber  bags  or  passed  through  long  rubber  tubes. 

Oxygen  can  be  purchased  in  cylinders,  or  it  can  be  made  by  heating 
a  mixture  of  pure  KC103  with  one-third  of  its  weight  of  Mn02  in  a 
250  c.c.  round-bottomed,  long-necked  flask  of  hard  glass  (Kjeldahl 
flask).  The  flask  should  be  surrounded  by  a  cylinder  of  wire  gauze  to 
protect  the  face  in  case  of  an  explosion.  The  mixture  must  be  tested 
for  carbon  by  first  heating  a  little  of  it  on  a  platinum  crucible  cover; 
it  should  not  sparkle  or  flash.  The  gas  so  made  will  contain  some 
chlorine  and  C02  which  must  be  removed  by  KOH  solution. 

The  Arrangement  of  the  Apparatus. — This  is  in  many  respects 
similar  to  that  used  in  the  determination  of  the  carbon  in  iron, 
except  that  as  the  water  is  to  be  weighed  as  well  as  the  CC>2,  tubes 
for  absorbing  it  are  added. 

The  train  comprises:  First,  a  gas  holder  for  the  oxygen.  The 
one  described  on  page  114  is  very  satisfactory.  About  500  c.c. 
of  oxygen  is  required  for  each  combustion. 

Where  only  an  occasional  combustion  is  made  a  simple  gas 
holder  can  be  made  of  a  couple  of  glass  bottles. 


254 


METALLURGICAL  ANALYSIS 


Second,  the  purifying  train  for  the  air  and  oxygen.  This  is 
made  in  duplicate,  as  described  under  the  determination  of  car- 
bon. The  bottle  containing  sulfuric  acid  absorbs  the  traces  of 
ammonia  or  its  salts  usually  present  in  the  air  of  a  laboratory. 
If  these  were  not  taken  out  they  would  burn  in  the  tube  and  form 
water  and  make  the  results  on  hydrogen  too  high.  As  it  is  as 
important  to  purify  the  air  from  moisture  as  from  CO2  in  this 
process  the  train  is  made  larger  and  separate  U-tubes  are  used 
for  the  soda  lime  and  the  CaCl2. 

Fig.  15  shows  the  details:  A  is  a  bottle  with  moderately  con- 
centrated H2SO4;  B  is  a  bottle  with  about  50  c.c.  of  KOH  solu- 
tion of  1.27  sp.  gr. ;  C  is  the  U-tube  with  the  soda  lime,  and  D  is 
the  U-tube  with  the  CaCl2. 

Third,  the  combustion  tube:  This  should  rest  on  asbestos  in 
the  trough  of  a  long  gas  combustion  furnace.  The  tube  should 


FIG.  15. 

be  made  of  the  best  infusible  glass  and  have  an  internal  diameter 
of  about  J^  in.  The  walls  of  the  tube  must  not  be  too  thick  or 
they  will  crack.  The  ends  of  the  tube  should  be  rounded  by 
heating  and  should  be  fitted. with  good  soft  corks,  well  rolled. 
Rubber  connections  with  this  tube  are  not  to  be  recommended, 
as  they  become  warm  and  are  liable  to  give  off  hydrocarbon 
vapor  and  to  absorb  some  CO2.  A  long  tube  and  furnace  are 
necessary.  The  writer  uses  a  furnace  with  twenty-five  burners 
and  a  tube  40  in.  long. 

The  tube  is  filled  as  follows:  A  space  of  5  to  5J^  in.  is  left 
empty  at  the  end  nearest  the  absorbing  train.  Then  follows: 
1.  A  plug  of  asbestos.  2.  Five  inches  of  fused  PbCrO4  in  small 
lumps.  3.  An  asbestos  plug.  4.  Twelve  to  14  in.  of  pure,  re- 
cently ignited  "wire"  CuO  (or  a  close  coil  of  fine  copper  gauze 
thoroughly  oxidized  by  heating  it  in  a  stream  of  pure  oxygen). 


THE  ANALYSIS  OF  COAL  AND  COKE 


255 


5.  An  asbestos  plug.  6.  The  "boat"  for  holding  the  coal.  There 
must  be  13  or  14  in.  of  empty  tube  following  the  last  asbestos  plug, 
so  that  the  part  of  the  tube  in  which  the  "boat"  is  placed  will  be 
well  in  the  furnace,  and  yet  the  tube  itself  projects  at  least  4  in. 
outside  of  the  furnace.  The  end  of  the  tube  is  connected  by  a 
cork,  glass  tube,  and  rubber  connection  with  the  purifying  train. 
The  cork  connections  in  the  ends  of  the  combustion  tube  must 
not  become  hot  enough  to  run  any  risk  of  being  burned;  hence  a 
sufficient  length  of  tube  must  project  from  the  furnace  at  each 
end.  These  projecting  ends  should  be  further  protected  from  the 
heat  of  the  furnace  by  discs  of  sheet  asbestos 
6  or  7  in.  in  diameter,  with  holes  in  the  cen- 
ter through  which  the  combustion  tube  passes. 

With  a  tube  arranged  as  above  it  is  not 
necessary  to  insert  a  copper  coil  behind  the 
"boat,"  as  is  sometimes  directed,  provided  the 
coal  is  slowly  heated  so  as  to  expel  the  volatile 
matter  gradually,  and  that  a  continuous  cur- 
rent of  air  or  oxygen  is  kept  passing  through 
the  tube,  so  as  to  prevent  the  products  of 
the  decomposition  from  working  back,  con- 
densing in  the  cool  part  of  the  tube,  and  so 
escaping  combustion. 

Fourth,  is  the  absorbing  train  following  the  combustion  tube, 
shown  in  Fig.  15,  and  consisting  of  G,  a  CaCl2  tube,  the  end  of 
which  is  inserted  into  the  cork  of  the  combustion  tube;  H,  Liebig 
potash  bulbs;  I,  a  soda-lime-calcium  chloride  tube  similar  to  that 
used  in  connection  with  the  potash  bulbs  in  the  determination  of 
carbon  in  iron;  J,  a  guard  tube  similar  to  I  but  reversed,  which 
is  connected  with  an  aspirator  for  drawing  air  through  the 
apparatus. 

A  "Mariotte  bottle,"  arranged  as  shown  in  Fig.  16,  makes  the 
best  aspirator.  The  suction  tube,  A,  passes  in  through  a  rubber 
stopper  at  the  top  and  reaches  nearly  to  the  level  of  the  run-out 
tube.  By  slipping  the  suction  tube  up  or  down,  the  suction  head 
can  be  regulated  so  as  to  barely  overcome  the  resistance  of  the 
train,  and  will  then  remain  exactly  the  same  as  long  as 
the  water  in  the  bottle  is  above  the  end  of  the  tube,  and  thus 
the  rate  of  aspiration  can  be  more  easily  kept  constant. 


FIG.  16. 


256  METALLURGICAL  ANALYSIS 

Testing  the  Apparatus. — First,  see  that  it  is  perfectly  tight 
by  starting  the  aspirator  and  shutting  off  the  entrance  of  air. 
Second,  heat  the  tube  red  hot  throughout  and  aspirate  two  liters. 
Detach  and  weigh  the  potash  bulbs  and  U-tube.  Connect  up 
again  and  aspirate  ^  liter  of  oxygen  and  then  2  liters  of  air. 
Detach  the  tubes  and  weigh.  There  should  be  neither  gain  nor 
loss  of  weight.  When  consecutive  weighings  are  found  to  agree 
within  0.5  mg.,  the  apparatus  is  ready  for  the  analysis. 

Process  of  Analysis. — Ignite  and  cool  the  boat.  Weigh  into  it 
0.2  gram  of  the  finely  pulverized  and  well-mixed  coal.  (The 
sample  must  be  made  very  fine,  lest  by  weighing  so  small  a  quan- 
tity average  results  will  not  be  obtained.)  Insert  the  boat  into 
its  proper  place  and  connect  up  the  apparatus.  Then  carefully 
heat  the  PbCrO4  to  dull  redness  and  the  CuO  to  bright  redness, 
drawing  a  slow  current  of  air  through  the  apparatus  all  the  time. 
Now  heat  the  tube  behind  the  coal  and  then  the  coal  itself, 
cautiously,  until  the  volatile  products  are  slowly  driven  off  and 
carried  forward  over  the  hot  CuO.  Then  introduce  oxygen, 
regulating  the  supply  so  as  to  avoid  too  vigorous  combustion 
and  consequent  fusion  of  the  ash,  which  will  lead  to  retention  of 
carbon.  After  the  carbon  is  all  burned,  which  is  shown  by  the 
sudden  disappearance  of  the  glow,  continue  the  oxygen  for  two 
minutes,  then  cut  it  off  and  aspirate  air.  Turn  off  the  gas  burn- 
ers and  let  the  tube  cool.  Continue  the  aspiration  until  1200  c.c. 
or  more  (at  least  seven  times  the  capacity  of  the  tube  and  absorb- 
ing train)  has  been  drawn  through.  Now  detach  the  absorption 
train  and  weigh.  The  increase  in  the  weight  of  the  CaCl2  tube 
gives  the  water  produced.  This  divided  by  9  gives  the  weight  of 
the  hydrogen  in  the  coal.  The  increase  in  the  CO2  apparatus 
is  the  CC>2;  three-elevenths  of  this  is  carbon.  The  apparatus  is 
now  ready  for  another  determination,  as  the  CuO  will  all  have 
been  reoxidized  by  the  air  current. 

The  aspiration  should  be  so  regulated  that  not  more  than  two 
or  three  bubbles  pass  through  the  potash  bulbs  per  second.  Dur- 
ing the  combustion  in  the  oxygen  the  gas  will  consist  largely  of 
CO2  and  will  be  almost  wholly  absorbed,  though  the  flow  of 
oxygen  into'the  apparatus  may  be  quite  rapid  at  the  time.  Care 
must  be  taken  that  the  oxygen  supply  is  sufficient  to  prevent 
back  suction  at  this  time. 


THE  ANALYSIS  OF  COAL  AND  COKE  257 

As  soon  as  the  CO2  is  absorbed  the  gas  may  begin  to  run 
through  the  potash  bulbs  too  rapidly  unless  the  gas  supply  is 
promptly  reduced. 

The  pressure  of  the  gas  in  the  tube  should  be  kept  near  that  of 
the  atmosphere.  This  can  be  accomplished  by  careful  regulation 
of  the  gas  and  the  aspirator. 

As  was  noted  in  the  determination  of  carbon  in  steel,  it  is 
desirable  to  reduce  the  necessary  aspiration  to  as  small  a  volume 
as  possible  by  using  small  connection  tubes  and  a  compact  train. 
This  saves  time  and  increases  accuracy. 

After  the  boat  containing  the  ash  is  withdrawn  from  the  tube, 
weigh  it.  The  ash  so  determined  should  agree  with  that  found 
in  the  proximate  analysis. 

The  tube  should  be  kept  carefully  closed  with  good  corks 
when  not  in  use.  A  train  and  tube  such  as  that  described  can  be 
used  for  months.  A  good  tube  of  Jena  glass,  while  it  may  twist 
out  of  shape  badly,  will  not  crack  or  blow  if  carefully  handled. 
Fifty  or  more  determinations  can  usually  be  made  on  one  filling 
of  the  tube. 

THE  DETERMINATION  OF  THE  NITROGEN  IN  CoAL1 

One  gram  of  the  very  finely  pulverized  coal  is  boiled  with  30 
c.c.  of  concentrated  H2S04,  7  grams  of  K2SO4  and  0.5  gram  of 
metallic  mercury  in  a  Kjeldahl  flask  until  the  carbon  is  com- 
pletely oxidized  and  the  liquid  is  nearly  colorless.  A  little 
potassium  permanganate  is  then  added.  When  the  liquid  is  cool 
it  is  largely  diluted  with  water,  the  mercury  precipitated  by  K2S 
and  the  ammonia  it  contains  determined  by  distillation  after 
adding  an  excess  of  solution  of  NaOH  with  cochineal  indicator. 
This  is  the  "  Kjeldahl  process,"  and  depends  on  the  fact  that  all 
the  nitrogen  is  converted  into  ammonia  by  the  treatment  with 
H2SO4.  For  a  complete  description  of  the  process,  see  Report 
of  the  Proceedings  of  the  Association  of  Official  Agricultural 
Chemists,  Bulletin  of  the  U.  S.  Department  of  Agriculture,  1895, 
No.  46.  The  results  on  coal  are  accurate,  provided  the  sample  is 
very  finely  pulverized  and  time  enough  given  in  the  digestion  to 
entirely  oxidize  the  coal.  This  may  take  two  or  three  hours. 

1  FIELDNER,  J.  Ind.  Eng.  Chem.,  VII,  106. 
17 


258  METALLURGICAL  ANALYSIS 

The  soda-lime  method  can  also  be  used  and  will  give  satisfactory  re- 
sults, provided  the  coal  is  completely  burned  and  the  soda-lime  heated 
in  the  tube  until  it  shows  no  more  black  color  and  leaves  no  unburned 
carbon  when  tested  by  solution  in  HC1.  For  a  description  of  this 
method,  see  Fresenius  Quantitative  Analysis. 

THE  OXYGEN  IN  COAL 

As  no  good  method  is  known  for  the  direct  determination  of  the  oxy- 
gen in  coal,  it  is  always  determined  by  difference,  the  sum  of  the 
percentages  of  H,  C,  N,  S,  and  ash  being  subtracted  from  100  and  the 
remainder  called  oxygen.  The  result  so  obtained  is  always  inaccurate, 
the  error  increasing  with  the  percentages  of  the  ash  and  sulfur.  The 
weight  of  the  ash  does  not  represent  that  of  the  mineral  matter  in  the 
coal,  the  pyrite  in  the  coal  being  burned  to  Fe203  and  the  sulfur  pass- 
ing off  as  SO  2.  Thus  4  atoms  of  S  in  2  FeS2  is  replaced  by  3  atoms  of 
0  in  the  Fe203,  and  the  loss  of  weight  is  equal  to  %  of  the  S.  For 
this  reason  many  chemists  use  %  S  instead  of  S  in  the  determination 
of  0  by  difference.  As  coals  contain  sulfur  in  other  forms  than  FeS2, 
and  also  frequently  other  compounds  that  lose  weight  on  burning,  such 
as  FeC03  and  CaC03,  it  is  doubtful  whether  the  results  obtained  in  this 
way  are  any  better  than  those  given  by  the  simple  formula  first  given. 

TESTING  A  COAL  AS  TO  THE  QUALITY  OF  THE  COKE 

In  order  to  obtain  the  analysis  of  the  coke  produced  from  a 
coal,  it  is  necessary  to  prepare  a  sample  of  the  coke.  This  can  be 
done  in  a  small  wind  furnace  as  follows :  Select  two  clay  crucibles 
of  such  a  size  that  one  will  set  easily  inside  of  the  other.  The 
writer  uses  a  Denver  fire  clay  "20-gram  assay"  crucible  for  the 
inner  and  a  large  " Hessian"  for  the  outer.  Grind  a  cover  onto 
the  inner  one  with  sand  until  it  fits  closely.  Put  the  larger  one 
in  the  furnace  and  let  it  get  bright  red  hot.  Meanwhile  charge 
the  smaller  with  100  grams  of  the  coal,  crushed  to  about  J^  in. 
mesh.  Cover  the  smaller  crucible  and  set  it  in  the  large  one, 
throw  a  little  coal  in  on  top  of  it,  and  then  carefully  cover  the 
larger  one.  At  the  end  of  an  hour  take  out  both,  put  a  little 
more  coal  into  the  outer  crucible,  and  then  let  them  cool  while 
covered.  When  cool,  take  out  the  inner  crucible  and  remove 
the  coke  from  it.  The  object  of  the  coal  in  the  outer  crucible  is 
to  prevent  oxygen  from  getting  into  the  coke  and  burning  out 
sulfur. 


THE  ANALYSIS  OF  COAL  AND  COKE  259 

THE  DETERMINATION  OF  THE  POROSITY  OF  COKE 

The  value  of  coke  as  a  blast-furnace  fuel  depends  somewhat  on  its 
porosity,  as  its  speed  of  combustion  will  increase  with  the  surface 
exposed  to  the  blast. 

The  porosity  is  usually  expressed  as  the  percentage  that  the  volume 
of  the  pores  forms  of  the  volume  of  the  coke. 

It  can  be  determined  by  weighing  the  coke  in  air  and  then  in  water, 
and  then  filling  the  pores  with  water  and  weighing  it  again. 

The  difficulty  of  filling  the  pores  with  water  is,  however,  so  great 
that  the  results  are  very  uncertain.  It  requires  long  boiling  in  water 
and  repeated  exhaustions  under  an  air  pump  to  remove  the  air;  and  as 
there  are  probably  pores  that  do  not  open  to  the  surface,  the  filling  is 
never  complete. 

The  following  method,  depending  on  the  determination  of  the  true 
specific  gravity  of  the  coke  substance  and  the  measurement  of  the 
volume  of  the  coke,  is  much  preferable.  It  is  essentially  that  published 
by  W.  C.  ANDERSON,  J.  Soc.  Chem.  Ind.,  XV,  p.  20. 

Determination  of  the  Specific  Gravity  of  the  Coke  Substance. — 

Into  the  neck  of  a  50  cc.  specific  gravity  bottle  put  a  glass  tube 
wide  enough  to  fit  air  tight  when  surrounded  with  a  collar  made 
of  a  rubber  tube.  The  glass  tube,  must  have  a  bulb  about  an 
inch  in  diameter  blown  in  it  just  above  the  bottle.  It  serves  to 
catch  and  return  anything  boiling  out  of  the  flask.  Weigh  into 
this  bottle  3.5  grams  of  the  pulverized  coke.  The  coke  must 
be  ground  in  a  Wedgewood  mortar  until  it  will  go  through  a 
40-mesh  sieve,  and  dried  at  100°C. 

Now  add  about  20  c.c.  of  water  to  the  bottle  and  set  it  on  a 
water  bath  for  15  minutes,  shaking  it  occasionally  till  the 
coke  powder  is  saturated.  Now  attach  to  the  tube  a  Bunsen 
suction  pump  giving  a  good  vacuum  and  exhaust  the  air  till  the 
liquid  boils  gently.  Continue  the  boiling  in  a  vacuum  for  two 
and  one-half  hours.  Remove  the  flask,  cool  it,  fill  it  up  with 
water,  and  weigh  as  usual  after  inserting  the  stopper. 

The  bottle  should  have  a  counterpoise,  of  course,  so  that  the 
weight  obtained  will  be  that  of  the  coke  and  the  water  only.  As 
the  bottle  holds  exactly  50  grams  of  water,  the  specific  gravity  of 
the  coke  will  be: 

W 
W  -  (W  -  .-)()) 


260  METALLURGICAL  ANALYSIS 

in  which  W  equals  the  weight  of  the  coke,  and  W  the  weight  of 
the  coke  and  water  together.  The  true  specific  gravity  of  coke 
taken  in  this  way  varies  from  1.75  to  2.00. 

The  Determination  of  the  Volume  or  Apparent  Specific  Gravity 
of  the  Coke  in  Lumps. — Several  average  lumps  should  be  selected 
and  broken  up  just  enough  to  exclude  any  large  mechanical 
fissures  or  cavities.  They  should  then  be  brushed  free  from  all 
dust  and  dirt  and  carefully  dried  and  weighed.  The  volume  of 
these  fragments  is  then  determined  by  measuring  the  amount  of 
water  they  displace. 

This  can  be  done  with  sufficient  accuracy  in  the  following 
simple  apparatus:  Take  a  pint  "  ointment  jar"  with  a  wide  mouth 
and  a  brass  or  aluminium  screw  cap.  Cut  a  gasket  of  sheet  rubber 
to  fit  over  the  end  of  the  jar,  so  that  the  top  will  screw  down  onto 
it  and  make  a  tight  joint.  The  end  of  the  jar  should  be  ground 
smooth.  Cut  a  small  hole  in  the  top  which  should  be  just  large 
enough  to  admit  the  stem  of  a  50  c.c.  pipette.  Screw  on  the 
top  and  fill  the  jar  with  water  till  it  runs  out  of  the  top  and  in- 
cludes no  air  bubbles.  Carefully  take  out  50  or  100  c.c.  of  the 
water  by  means  of  a  pipette  put  in  through  the  hole  in  the  top. 
Now  unscrew  the  top,  put  in  50  or  100  grams  of  the  weighed 
lumps  of  coke,  shake  them  around  to  loosen  air  bubbles,  replace 
the  cap  on  the  jar  and  run  in  water  from  a  burette  until  the  water 
comes  exactly  to  the  level  of  the  hole.  The  difference  between 
that  measured  out  with  the  pipette  and  that  measured  back 
in  with  the  burette,  will  be  the  volume  of  the  coke  in  cubic 
centimeters. 

To  find  the  volume  of  the  pores  in  the  coke,  subtract  its  weight 
divided  by  its  true  specific  gravity  from  the  volume  of  the  coke 
as  determined  above.  The  percentage  that  the  pores  form  of  the 
total  volume  of  the  coke  will  be: 

/  wt.  of  the  coke     \ 

\      "  vol.  of  coke  X  sp.  gr./ 

TESTING  THE  EFFECT  OF  " WASHING"  ON  COAL 

The  object  of  the  washing  of  coal  on  jigs  or  other  washers  is  the  reduc- 
tion of  the  ash  and  the  sulfur  in  the  coal.  The  benefit  that  a  given 
coal  will  receive  in  the  process  will  depend  upon  the  form  in  which 


777 K  ANALYSIS  OF  COAL  AND  COKE  261 

these  impurities  occur  in  it.  Only  the  ash  that  is  due  to  intermixed 
slate  and  the  sulfur  that  is  in  the  form  of  free  pyrite  can  be  removed 
by  the  process,  which  depends  upon  the  difference  in  the  specific  gravity 
between  these  materials  and  the  coal.  The  fineness  to  which  the  coal 
must  be  crushed  in  order  to  effect  a  satisfactory  breaking  apart  of  the 
heavy  and  light  material  will  depend  upon  the  nature  of  the  coal  seam. 
The  finer  the  coal  has  to  be  crushed  the  greater  will  be  the  loss  of  coal 
in  the  slimes.  All  these  points  can  be  investigated  in  the  laboratory. 

The  operation  consists  in  crushing  the  coal  to  some  determined 
maximum  size,  then  separating  it  into  a  series  of  sizes  by  sieves,  and 
finally  separating  these  sizes  into  their  heavy  and  light  components. 

The  specific  gravity  of  coal  is  less  than  1.35  while  that  of  the  impuri- 
ties is  always  above  this  figure;  hence  the  separation  into  light  and 
heavy  parts  can  be  made,  as  suggested  by  Dr.  Drown,  by  mixing  the 
coal  with  a  solution  of  CaCU,  of  1.35  sp.  gr.,  in  which  the  coal  will 
float  and  in  which  the  impurities  will  sink. 

The  apparatus  needed  consists  of,  first,  a  set  of  sieves  of  J£, 
y±  and  J^o  m-  niesh;  second,  a  " miner's  pan"  or  some  equiva- 
lent in  which  a  small  quantity  of  material  can  be  washed;  third, 
a  solution  of  calcium  chloride  of  1.35  sp.  gr.,  made  by  dissolving 
1  Ib.  of  crude  CaCl2  in  a  pint  of  water,  and  when  the  solution 
has  cooled,  diluting  it  to  exactly  the  right  gravity. 

The  coal  is  crushed,  avoiding  the  production  of  dust  as  far  as 
possible,  until  it  will  all  pass  through  the  half-inch  sieve.  The 
sample  is  then  thoroughly  mixed  and  a  weighed  amount  of  it 
(from  3  to  5  kg.)  sifted  over  the  quarter-inch  and  the  twentieth- 
inch  sieves.  This  divides  it  up  into  sizes  J£  to  J£,  J4  to  J^o 
and  J^o  to  dust.  The  quantity  in  each  size  is  then  weighed 
and  expressed  in  percentages  of  the  whole.  The  two  larger 
sizes  are  now  separated  in  the  chloride  of  calcium  solution  as 
follows:  A  beaker  holding  about  a  liter  is  nearly  filled  with  the 
solution,  the  coal  put  into  it  a  little  at  a  time  and  well  stirred 
to  thoroughly  wet  it  and  detach  all  air  bubbles.  The  coal 
rises  to  the  surface,  while  the  slate  and  pyrite  settle  to  the  bot- 
tom. Enough  of  the  coal  should  be  put  in  at  a  time  to  make  a 
layer  about  an  inch  thick  when  it  rises  to  the  top.  This  is  now 
skimmed  out  with  a  little  dish  or  a  dipper  and  dropped  into  a 
large  funnel,  the  neck  of  which  is  closed  with  a  small  perforated 
porcelain  disc.  More  coal  is  now  added  to  the  solution  and  the 
operation  continued  until  all  of  the  given  size  is  thus  separated. 


262  METALLURGICAL  ANALYSIS 

The  coal  in  the  funnel  is  then  thoroughly  cleaned  from  chloride  of 
calcium  by  pouring  water  over  it,  allowed  to  drain,  then  spread 
out  on  paper,  air  dried  and  weighed.  The  chloride  of  calcium 
solution  is  then  carefully  poured  off  from  the  heavy  material  in 
the  beaker,  which  is  then  washed  out,  dried  and  weighed.  The 
material  finer  than  %o  m-  is  washed  in  the  miner's  pan.  The  coal 
is  stirred  up  in  water  in  the  pan,  and  then  by  rocking  the  pan  care- 
fully the  lighter  portion  is  floated  off  and  can  be  caught  in  a  large 
dish  where  it  is  allowed  to  settle.  The  water  is  decanted  off 
and  the  material  air  dried  and  weighed.  The  slate  and  pyrite 
left  in  the  pan  are  also  collected,  dried  and  weighed.  Each  of 
the  above  products  should  then  be  analyzed  for  ash  and  sulfur. 
As  a  check,  the  analysis  of  the  original  coal  should  be  computed 
from  the  analyses  of  these  products  and  should  agree  very  closely 
with  that  of  the  original  sample.  The  lighter  products  from 
the  pan  may  be  stirred  up  in  water,  and  the  portions  settling 
in  about  one  minute  separately  weighed.  The  fine  stuff  floating 
off  is  determined  by  difference,  and  will  constitute  approximately 
the  coal  lost  in  washing. 

A  little  practice  is  necessary  in  order  to  properly  manipulate  the 
pan;  but  the  treatment  of  the  fine  stuff  in  the  CaCl2  solution  is  very 
unsatisfactory,  and  as  it  forms  only  a  small  portion  of  the  whole, 
inaccuracies  in  the  panning  will  have  little  effect.  From  a  comparison 
of  the  results  shown  on  the  various  sizes,  it  may  be  desirable  to  repeat 
the  experiment,  crushing  the  whole  of  the  coal  to  y±  in.  or  even  to 
y%  in.  in  order  to  separate  very  finely  disseminated  pyrite  and  secure 
a  coal  low  in  sulfur.  But  as  the  loss  in  washing  falls  almost  wholly 
on  the  finer  coal,  the  increase  of  the  proportion  passing  the  smallest 
sieve  must  be  carefully  noted. 

If  the  coal  is  crushed  to  smaller  sizes  and  then  separated  in  the 
solution,  all  the  finest  dust  must  be  first  sifted  out  on  a  60-  or  80-mesh 
sieve,  or  it  will  clog  up  the  filters  and  prevent  the  draining  off  of  the 
solution.  The  dust  can  then  be  panned  as  usual. 

REFERENCES: 

See  DROWN,  Trans.  Am.  Inst.  Mining  Engrs.,  XIII,  p.  341. 
STOEK,  J.  Soc.  Chem.  Ind.,  1897,  p.  304. 

THE  DETERMINATION  OF  THE  HEATING  POWER  OF  COAL 

By  the  heating  power  of  a  fuel  is  meant  the  total  amount  of  heat 
produced  by  the  complete  combustion  of  the  unit  weight  of  the  fuel, 


THE  ANALYSIS  OF  COAL  AND  COKE  263 

In  order  to  simplify  calculations  in  technical  work  it  is  convenient 
to  define  the  unit  of  heat  as  the  heat  required  to  raise  the  unit  weight 
of  water  the  unit  of  temperature.  If  the  unit  of  weight  is  the  gram 
and  the  unit  of  temperature  the  degree  Centigrade,  the  unit  of  heat  is 
the  calorie.  If  the  units  are  the  pound  and  the  degree  Fahrenheit,  the 
heat  unit  is  the  British  thermal  unit. 

With  the  heat  unit  defined  as  above,  the  number  expressing  the 
heating  value  of  a  fuel  will  be  the  same,  whatever  the  unit  of  weight 
adopted,  as  long  as  the  unit  of  temperature  is  unchanged.  If  the 
unit  of  temperature  is  changed,  as,  for  instance,  from  Centigrade  to 
Fahrenheit,  the  figure  for  the  heating  value  will  simply  have  to  be 
changed  in  the  inverse  ratio  of  the  dimensions  of  the  units. 

In  the  example  quoted,  as  the  ratio  of  the  degree  C.  to  the  degree  F. 

100 
is  YOQI  heating  powers  in  calories  can  be  converted  into  heating  powers 

180 
in  B.t.u.  by  multiplying  them  by  ,  ^'  or  %. 

The  heating  power  of  coke,  anthracite  and  bituminous  coal  can  be 
calculated  with  sufficient  accuracy  for  many  purposes  from  the  ultimate 
analysis  by  Dulong's  formula,  as  follows : 

Heating  power  =  8080°C.+34,460(H-^0)-f  2250  S. 

On  the  fuels  specified  the  results  by  this  formula  rarely  differ  more 
than  2  per  cent,  from  those  obtained  with  the  calorimeter. 

Where  accurate  determination  of  the  heating  value  is  required,  the 
direct  combustion  in  the  bomb  calorimeter  should  be  made. 

For  a  description  of  the  several  forms  of  this  instrument,  the  methods 
of  using  them,  and  the  precautions  necessary  in  order  to  secure  accurate 
results,  see  "Fuel"  by  Herman  Poole;  Mahler,  Bulletin  de  la  Societe  de 
L'Encouragement  de  L'Industrie;  Berthelot,  Mechanic  Chemique,  and 
Longuimine,  Bestimmung  der  Verbrennungs  Warme. 

For  a  complete  description  and  discussion  of  the  determination  of 
the  calorific  value  of  coals  see  "Coal,"  by  Professor  E.  E.  Sommermeier, 
McGraw-Hill  Book  Co.,  publishers. 


CHAPTER  XXXI 
THE  ANALYSIS  OF  GASES 

The  analysis  of  the  following  kinds  of  gases  will  be  described:  flue  or 
chimney  gases,  blast-furnace  gases  and  producer  gas,  coke  oven  and 
natural  gases,  mine  air.  Of  course  the  composition  of  any  kind  of 
gas  may  vary  greatly  but  the  following  analyses  are  typical : 


Chirr 

ney  gas 

Blast-furnace 
gas 

Producer 

gas 

Natural 
gas 

Coke  oven 
gas 

CO2 

8.6% 

CO2  13.5% 

CO2     6.3% 

CO2      0.2% 

CO2      2.0% 

02 

10.3 

O2       0.0 

C2H4    0.6 

CH4  85.3 

C2H4    1.9 

CO 

0.2 

CO    25.5 

O2        0.0 

C2H612.5 

O2        0.3 

N2 

80.9 

H2       3.0 

CO     23.7 

N2        2.0 

CO       6.4 

CH4    0.2 

H2      11.1 

H2      56.3 

N2     57.8 

CH4     2.6 

CH4   19.0 

N2      55.7 

C2H6    2.0 

N2      12.1 

Mine  air  is  simply  air  containing  more  or  less  CO 2,  CH4  and  possibly 
CO.  The  gases  are  grouped  as  above  because  the  analysis  of  the  gases 
in  the  different  groups  calls  for  special  procedure.  The  methods 
given  are  methods  in  wide  technical  use. 

It  must  not  be  forgotten  that  the  results  obtained  by  measuring  the 
reduction  in  volume  of  a  gas  sample  when  its  constituents  are  absorbed 
are  the  results  on  the  dry  basis  although  the  gas  in  the  apparatus  is 
saturated  with  water  vapor.  The  reason  is  that  when  a  given  constitu- 
ent is  absorbed  the  water  vapor  corresponding  to  the  amount  of  the 
constituent  absorbed  at  the  same  time  condenses,  since  with  constant 
temperature  the  aqueous  tension  in  the  remaining  gas  remains  constant. 

Further,  if  the  gas  contains  tar  or  heavy  hydrocarbon  vapors  in 
the  hot  main,  these  will  condense  more  or  less  completely  when  the 
sample  is  taken  and  will  not  be  obtained  in  the  analysis.  They  must 
be  determined  by  special  methods. 

Any  change  in  the  temperature  of  the  gas  during  analysis  will  produce 
error  in  two  ways,  first,  according  to  the  law  that  the  volume  of  a  gas 
is  proportional  to  its  absolute  temperature;  second,  because  of  the 

264 


THE  ANALYSIS  OF  GASES  265 

fact  that  any  change  in  temperature  will  change  the  aqueous  tension 
in  a  gas  standing  over  water.  Thus  if  100  c.c.  of  gas  at  20°C.  and  745 
mm.  pressure  suffers  a  drop  of  2°  in  temperature  the  final  volume  will  be 

291  743 

c.c.     So    that    under  these   conditions   a   gas 


having  no  C02  would  if  analyzed  for  C02  show  0.95  per  cent.  C02  unless 

291 
the  correction  were  made.     The  factor  ^QQ  is  simply  the  ratio  of  the  ab- 

743 
solute  temperature  and  the  factor  ^^  is  the  ratio  of  the  atmospheric 

pressure  minus  the  drop  in  aqueous  tension  to  the  atmospheric  pressure. 
The  general  formula  is, 

T'     P  +  a 
V  =  V  X  ip  X  —  p-  .     V  is  the  original  volume,  V  is 

the  volume  sought,  T  is  the  original  absolute  temperature,  T'  is  the 
new  absolute  temperature,  P  is  the  barometric  pressure  and  a  is  the 
change  in  aqueous  tension. 

THE  ANALYSIS  OF  FLUE  GAS 

Flue  gas  contains  CO  2,  02,  CO,  N2,  and  sometimes  small  percentages 
of  S02  and  hydrocarbons,  and  traces  of  oxides  of  nitrogen.  The  gas 
is  usually  saturated  with  water  vapor,  but  this  is  not  considered  in  the 
analysis,  which  refers  only  to  the  dry  gas.  The  percentage  of  water 
in  the  saturated  gas  can  be  calculated  from  the  temperature  ;  if  the  gas 
is  not  saturated,  its  "dew  point"  (the  temperature  at  which  moisture 
begins  to  condense  from  the  gas)  must  be  taken,  and  the  tension  of  the 
water  vapor  it  contains  found  from  this.  If  the  temperature  of  the 
gas  is  above  the  boiling-point  of  water,  draw  a  measured  volume  of  it 
through  a  condenser,  taking  the  temperature  of  the  saturated  gas  as  it 
comes  out 

Weigh  the  water  collected  from  the  condenser  and  add  to  it  the 
moisture  remaining  in  the  gas,  as  calculated  from  its  temperature 
after  the  cooling.  Or  draw  the  gas  through  a  weighed  calcium  chloride 
tube  and  determine  the  increase  in  weight,  after  filtering  out  the  dust 
by  passing  the  gas  through  a  tube  packed  with  asbestos  kept  at  100°C. 

Only  the  C02,  CO  and  O2  are  usually  determined  in  flue  gas,  the  re- 
mainder being  considered  as  N2.  But  any  thorough  investigation  of 
a  flue  gas  would  require  the  determination  of  hydrogen  and  methane. 

In  making  the  analysis,  a  measured  volume  of  the  gas  is  treated 
successively  with  a  series  of  reagents  that  absorb  the  several  constituents, 
the  remaining  volume  being  measured  after  each  absorption.  The  gas 


266  METALLURGICAL  ANALYSIS 

is  measured  in  a  graduated  tube,  which  must  be  surrounded  with  a 
water  jacket  to  keep  the  temperature  constant  during  the  time  taken  for 
the  analysis. 

The  gas  is  always  measured  at  the  atmospheric  pressure.  As  the  time 
taken  for  the  analysis  is  very  short,  it  is  assumed  that  the  temperature 
and  the  barometer  remain  constant  during  the  period.  However,  a 
thermometer  should  be  suspended  in  the  water  jacket  and  several  obser- 
vations made. 

Sampling  the  Gas. — The  gas  should  be  drawn  from  the  flue  by  a 
pipe  that  crosses  it  at  right  angles  and  extends  to  within  6  in.  of  the 
further  wall.  The  end  of  the  tube  should  be  closed  with  a  cap,  and 
the  gas  should  be  drawn  into  it  through  a  number  of  holes  about  He 
in.  in  diameter,  drilled  along  the  side  of  the  tube  at  regular  intervals  not 
greater  than  6  in.  The  nearest  holes  should  not  be  less  than  6  in.  from 
the  side  of  the  flue.  The  diameter  of  the  tube  should  be  at  least  twelve 
times  the  diameter  of  the  holes  in  the  side.  This  will  insure  a  uniform 
sampling  across  the  flue. 

Professor  Lord  carefully  tested  this  point  by  inserting  such  a  tube  in 
air  and  gas  for  different  portions  of  its  length  and  analyzing  the  gas 
drawn  from  the  tube.  The  composition  of  the  issuing  mixture  was 
always  proportional  to  the  number  of  holes  in  the  gas  and  in  the  air,  air 
and  gas  being  under  atmospheric  pressure. 

The  sampling  tube  can  be  made  of  iron,  if  the  temperature  of  the 
flue  does  not  exceed  340°C.,  as  at  that  temperature  iron,  even  if  rusted 
or  covered  with  soot,  is  without  action  on  flue  gas,  neither  the  CO  nor 
the  C(>2  being  affected.  This  point  was  tested  by  the  writer  by  passing 
flue  gas  containing  CO  through  a  glass  tube  filled  with  iron  tacks,  also 
with  rusted  tacks  and  with  soot  and  tacks.  The  tube  was  immersed  in 
a  bath  of  melted  lead  and  the  temperature  of  the  lead  measured  by  a 
nitrogen-filled  high  temperature  thermometer.  If  soot  and  rust  are  pres- 
ent on  the  iron,  action  begins  about  340°C.,  and  is  rapid  at  400°C.,  CO 
being  oxidized  by  the  Fe20a  and  oxygen  consumed  by  the  soot,  forming 
C02.  With  clean  iron,  however,  there  is  practically  no  action  at400°C. 
As  340°C.  is  above  the  temperature  at  which  most  flue  or  blast-furnace 
gas  is  drawn  off,  the  use  of  iron  tubes  is  generally  permissible.  For  flue 
temperature  higher  than  340°C.,  water-cooled  tubes  must  be  used  for 
withdrawing  the  samples.  For  rapidly  withdrawing  a  single  sample 
from  the  interior  of  a  furnace,  an  iron  tube,  open  at  the  end  and  wrapped 
with  Y±  in.  of  sheet  asbestos  tied  on  with  wire,  can  be  used.  The  asbes- 
tos cover  is  well  soaked  with  water  and  the  tube  run  into  the  furnace  and 
the  sample  drawn.  A  tube  so  protected  can  remain  in  a  white  hot  fur- 
nace for  two  or  three  minutes  without  the  asbestos  drying  or  the  tube 
heating  beyond  a  safe  point.  A  silica  tube  is  convenient  for  sampling 


THE  ANALYSIS  OF  GASES  267 

gases  from  a  very  hot  place  such  as  at  the  ports  of  an  open-hearth  fur- 
nace. Where  there  is  a  strong  draft,  as  in  a  chimney  flue,  it  is  important 
that  the  opening  by  which  the  tube  passes  through  the  wall  be  well 
plastered  up  with  clay,  or  air  may  be  drawn  in  and  reach  the  nearer  holes 
and  affect  the  sample.  From  the  end  of  the  sampling  tube  the  gas  is 
drawn  continuously  by  a  water  or  steam  aspirator.  If  the  gas  sample  is 
to  be  kept  any  time  before  analysis,  it  must  be  borne  in  mind  that  gases 
containing  CC>2  cannot  be  preserved  over  water,  as  the  CC>2  is  rapidly 
absorbed.  If  confined  over  water  the  water  should  be  covered  with 
paraffin  shavings.  The  writer  has  found  that  if  the  water  be  well 
covered  with  paraffin  shavings  a  sample  of  gas  with  10  per  cent.  CC>2  will 
not  lose  0.10  per  cent.  C02  in  three  hours. 

In  most  cases  it  is  possible  and  far  preferable  to  make  the  analysis 
at  the  furnace,  especially  where  a  series  of  analyses  is  required.  Where 
this  is  not  possible,  as,  for  instance,  on  a  locomotive  engine  test,  the 
apparatus  shown  in  Fig.  17  will  be  found  very  effective  and  convenient 
for  drawing  a  series  of  samples  at  short  intervals. 

The  sample  tube,  F,  f,  has  a  capacity  of  about  250  c.c.;  the  ends  are 
closed  with  rubber  tubes  stopped  with  short  glass  rods  J.  A  number  of 
these  sample  tubes  are  provided;  they  are  kept  in  a  rack  in  a  box,  and 
are  filled  with  water  before  starting  out.  In  the  apparatus  itself  A  is  a 
bottle  of  about  a  liter  capacity,  containing  absorbent  cotton  to  filter  the 
gas.  C  is  a  small  bottle  containing  a  little  mercury;  it  serves  as  a  trap  to 
prevent  reversal  of  the  gas  current.  The  gas  enters  through  E,  and  is 
drawn  out  through  D  by  an  aspirator  at  the  rate  of  about  150  c.c. 
a  minute. 

Thus  the  bottle,  A,  will  always  contain  a  gas  representing  the  average 
of  several  minutes.  H  is  a  "pressure  bottle,"  connected  as  shown. 

In  taking  the  sample  the  apparatus  is  set  up  as  shown;  the  gas  is 
supposed  to  be  flowing  freely  through  the  bottles  A  and  D.  A  pinch- 
cock  (not  shown)  on  the  rubber  connection  between  the  Y  tube  and  the 
sample  tube  is  opened  and  gas  drawn  in  by  lowering  the  pressure  bottle, 
H,  until  the  gas  fills  the  tube  and  also  the  lower  tube,  G.  The  cock  is 
then  closed  and  the  pressure  bottle  lifted,  so  as  to  put  the  confined  gas 
under  a  little  pressure;  but  the  lower  tube,  G,  must  contain  gas  enough 
to  prevent  any  water  getting  into  the  sample  tube.  The  rubber  connec- 
tion with  F  is  now  pinched  tight  and  the  tube  disconnected.  It  is  then 
closed  by  inserting  the  glass  rod  into  the  rubber.  The  lower  end  is 
closed  in  the  same  way.  The  rubber  tubes  and  stoppers  on  the  sampling 
tube  can  be  wired  if  necessary  to  keep  them  tight.  As  the  gas  is  under  a 
little  pressure,  any  leakage  during  the  disconnection  will  be  out  from  and 
not  into  the  gas. 


268 


METALLURGICAL  ANALYSIS 


The  tube  is  now  replaced  by  a  second  one  and  the  apparatus  is  ready 
for  drawing  a  new  sample. 

Fig.  18  shows  a  convenient  arrangement  for  drawing  a  single  sample 
rapidly,  as,  for  example,  through  an  asbestos-covered  pipe  such  as  was 
described. 

The  bottle  C  contains  a  little  mercury  and  serves  as  a  trap.  The 
bottles  A  and  B  contain  brine  covered  with  paraffin  shavings  P.  The  gas 
delivery  tube  is  connected  with  the  tube  F.  B  is  filled  with  water  by 
raising  A,  the  air  escaping  through  the  mercury  in  C.  Now  A  is  lowered 


FIG.  17. 


FIG.  18. 


and  the  gas  drawn  in  through  F,  the  mercury  preventing  any  return 
through  E.  In  this  way  the  gas  can  be  drawn  and  emptied  till  all  air  is 
expelled,  and  then  the  bottle  B  filled  and  the  pinch-cock  D  closed  and  the 
sampler  removed.  The  bottles  may  be  of  large  capacity  so  that  the 
sample  may  be  taken  over  many  minutes.  The  water  in  B  should  be 
shaken  with  some  of  the  gas  in  order  to  become  saturated  with  it. 

If  it  is  desired  to  draw  a  sample  continuously  for  several  hours,  the 
apparatus  shown  in  Fig.  19  can  be  used.  It  will  draw  a  sample  at  a 
nearly  fixed  rate  per  minute  for  several  hours.  It  should  be  filled  with 


THE  ANALYSIS  OF  GASES 


269 


similar  gas  for  some  days  and  then  emptied  before  use,  as  a  new  metal 
gas  holder  affects  the  sample  a  little  at  first. 

The  gas  is  drawn  into  the  tank,  A,  through  the  cock,  G,  by  the  escape 
of  the  water  at  the  bottom  through  the  tube,  B.  The  rate  of  this 
escape  is  kept  uniform  by  the  floating  siphon,  E,  in  the  connecting 
cylinder,  C.  The  tube,  B,  is  large,  so  that  the  level  of  the  water  in  the 
tank  and  the  cylinder  is  the  same,  and  the  rate  of  flow  from  the  latter  is 
regulated  by  the  constant  head 
of  the  floating  siphon  carried  by 
the  float,  D. 

In  analyzing  the  flue  gas  on 
boiler  tests,  one  sample  should 
be  taken  every  30  minutes.  This 
will  give  a  fairly  accurate  average 
for  the  period  of  10  hours  usually 
covered  by  the  test.  Experi- 
ments made  by  Mr.  F.  Hass  in 
the  Department  of  Metallurgy, 
Ohio  State  University,  showed 
practically  no  difference  in  the 
results  obtained  by  averaging 
samples  taken  every  30  minutes 
and  every  15  minutes  for  10 
hours.  Samples  taken  in  the 
continuous  sampler  above  de- 
scribed always  show  less  C02,  but 
otherwise  agree  closely  with  the 
average  of  the  half -hour  samples 
covering  the  same  10  hours,  pro- 
vided they  are  analyzed  promptly. 
If  the  sample  in  the  tank  is  al- 
lowed to  stand  for  some  time,  the  FIG.  19. 
loss  of  C02  with  a  corresponding 

increase  of  nitrogen  and  oxygen  may  be  very  marked.  The  follow- 
ing two  analyses  illustrate  the  comparison  for  a  10-hour  test.  It  shows 
the  loss  of  CO  2. 


Average  of  30- 
minute  samples 

Gas  from  tank 

CO2 

11    1 

10.4 

O2 

8  0 

8.25 

CO  

0.43 

0.30 

N«. 

80.47 

81.05 

270 


METALLURGICAL  ANALYSIS 


Apparatus. — The  Orsat's  apparatus  is  rapid  and  convenient-  for 
the  analysis  of  flue  gas,  although  the  writer  prefers  the  Hem  pel 
outfit,  except  when  the  apparatus  must  be  carried  around. 
Orsat's  apparatus  is  shown  as  connected  for  use  in  Fig.  20.  The 
gas  from  the  flue  is  drawn  into  the  bottle  B  through  the  tube  A. 
B  contains  absorbent  cotton  to  filter  out  soot  from  the  gas. 
From  B  the  gas  passes  down  into  the  bottle  D,  where  it  bubbles 
through  about  an  inch  of  water  and  then  goes  through  F  to  the 


FIG.  20. 

aspirator.  If  the  rate  of  aspiration  is  about  150  c.c.  a  minute, 
and  the  bottle  B  of  500  c.c.  capacity,  D  will  contain  a  sample  of 
the  gas  representing  the  average  of  some  minutes.  D  is  connected 
with  the  analyzing  apparatus  as  shown.  In  the  apparatus  P 
is  the  gas  measuring  tube.  Q  is  the  water  jacket.  S  shows  the 
glass  stop-cock  that  connects  the  gas  tube  with  the  reagent  tubes, 
I,  H,  and  G.  These  contain  short  lengths  of  glass  tube  to  spread 
out  the  liquid  and  increase  the  active  surface. 


THE  ANALYSIS  OF  GASES  271 

I/  and  M  are  bottles  arranged  as  a  water  seal  to  keep  the  air 
from  the  reagents  in  the  tubes;  they  are  connected  with  the  rear 
bulbs  of  the  tubes  as  shown.  R  is  a  three-way  cock  that  serves 
to  empty  the  gas  from  the  apparatus.  O  is  the  pressure  bottle 
for  manipulating  the  gas  in  the  measuring  tube. 

The  apparatus  should  be  protected  from  drafts  of  cold  air,  but, 
as  the  analysis  is  completed  in  15  minutes,  the  water  jacket  on  the 
measuring  tube  will  prevent  any  appreciable  change  in  tempera- 
ture if  ordinary  care  is  used.  All  the  stop-cocks  should  be  well 
greased  with  vaseline.  Two  or  three  drops  of  H2SC>4  should  be 
added  to  the  water  in  the  pressure  bottle,  as  this  prevents  it 
from  becoming  slightly  alkaline  and  absorbing  C02. 

The  water  in  the  pressure  bottle  must  be  saturated  with  the 
gas  to  be  analyzed,  to  prevent  its  acting  on  the  sample.  This 
is  best  done  by  running  several  analyses  before  the  regular  work 
begins.  This  will  bring  the  water  to  a  condition  of  saturation 
with  the  average  gas  and  render  it  practically  non-absorbing  to 
the  gas  analyzed.  Once  in  this  condition  the  water  can  be  used 
indefinitely.  If  new  water  is  put  in,  the  saturation  must  be  re- 
peated. The  water  in  the  pressure  bottle  must  be  at  the  same 
temperature  as  that  in  the  burette  jacket. 

Preparation  of  the  Reagents. — KOH  solution.  Dissolve  100 
grams  of  the  best  quality  potassium  hydroxide  in  300  grams  of 
water.  Let  the  solution  stand  in  a  closed  bottle  till  any  oxide 
of  iron  settles,  and  use  only  the  clear  solution.  It  is  best  to 
prepare  a  quantity  of  this  and  keep  it  some  time  before  use. 
Carbon  dioxide  is  easily  and  rapidly  absorbed  in  the  KOH 
forming  K2COs. 

Potassium  Pyrogallate. — This  is  the  best  absorbent  for  oxygen. 
Phosphorus  is  also  frequently  used  but  it  is  too  easily  "  poisoned  " 
so  that  it  will  not  work.  The  writer  always  prefers  the  pyro- 
gallate.  It  is  made  by  dissolving  15  grams  of  pyrogallic  acid, 
C6H3(OH)3,  in  100  c.c.  of  a  solution  of  KOH,  sp.  gr.  1.55. 
The  solution  will  absorb  about  20  c.c.  of  oxygen  per  cubic  centi- 
meter.1 It  acts  rapidly  at  first  but  as  it  becomes  saturated  with 
oxygen  it  acts  more  slowly.  The  relation  of  the  pyrogallic  acid 
to  the  alkali  is  important,  for,  if  the  concentration  of  alkali  is 
too  low,  some  CO  may  be  given  off  when  oxygen  is  absorbed. 

1  ANDERSON,  J.  Ind.  Eng.  Chem.,  VII,  587. 


272  METALLURGICAL  ANALYSIS 

The  solution  as  above  made  will  not  evolve  CO.  At  tempera- 
tures above  15°C.  the  absorption  is  rapid,  the  oxygen  in  100  c.c. 
of  air  being  absorbed  in  three  minutes,  but  at  lower  temperatures 
the  absorption  is  much  slower.  Of  course  CO2  will  be  absorbed 
in  this  solution  and  it  must  be  previously  removed  with  KOH. 
If  the  gas  contains  only  a  little  oxygen  the  pyrogallate  solution 
is  best  made  by  dissolving  15  grams  of  pyrogallic  acid  in  150  c.c. 
of  30  per  cent.  KOH. 

Ammoniacal  Cuprous  Chloride. — Dissolve  450  grams  of  am- 
monium chloride  and  400  grams  of  cuprous  chloride  in  1500  c.c. 
of  water.  For  use  the  solution  is  diluted  with  one-third  its 
volume  of  ammonia  water,  sp.  gr.  0.9.  Some  metallic  copper 
should  be  kept  in  the  solution  to  keep  it  active.  One  cubic 
centimeter  will  absorb  about  16  c.c.  of  CO.  The  reaction 
is  2CuCl+2CO  =  Cu2Cl22CO.  However,  this  compound  is  very 
unstable  and  after  a  certain  amount  of  it  has  been  formed  in 
the  solution  it  begins  to  decompose  and  to  give  up  CO.  Con- 
sequently in  all  work  where  much  accuracy  is  required  it  is 
absolutely  necessary  that  the  .greater  part  of  the  CO  be  first  ab- 
sorbed in  one  cuprous  chloride  pipette  and  then  the  remaining 
CO  be  absorbed  in  a  pipette  containing  freshly  prepared  cuprous 
chloride  solution.  The  second  one,  after  it  has  been  used  a  num- 
ber of  times,  is  made  the  first  and  a  fresh  supply  is  put  in  the  second. 

The  cuprous  chloride  also  absorbs  oxygen,  hence  the  oxygen 
in  the  sample  must  be  removed  before  the  CO  is  absorbed  in  the 
cuprous  chloride.  Cuprous  chloride  will  also  absorb  acety- 
lene, ethylene,  etc. 

To  fill  the  apparatus :  Remove  the  old  solution  by  first  driving 
air  over  the  gas  tube  into  the  absorbing  bulbs.  This  is  done  by 
raising  the  pressure  bottle  and  forcing  the  liquid  all  into  the  rear 
bulbs.  Then  empty  each  by  a  small  siphon  first  filled  with  water 
and  inserted  to  the  bottom  of  the  bulb.  Now  fill  the  first  rear 
bulb,  J,  with  the  KOH  solution.  This  serves  to  absorb  CO2  and 
also  SO2  and  H2S.  It  acts  rapidly  and  completely  and  one  filling 
will  serve  for  from  fifty  to  sixty  gas  analyses  before  its  action 
begins  to  be  too  slow. 

Put  a  good-sized  funnel  into  the  second  rear  bulb  and  weigh 
into  it  30  grams  of  pyrogallic  acid.  Wash  this  down  into  the 
bulb  with  200  c.c.  of  KOH  solution.  If  the  apparatus  will  not 


THE  ANALYSIS  OF  GASES  273 

hold  the  volume  of  solution,  take  less  and  reduce  the  pyrogallic 
acid  proportionately;  if  it  requires  more  add  more. 

The  third  bulb  is  filled  with  the  cuprous  chloride  solution. 
The  glass  tubes  in  this  bulb  contain  spirals  of  copper  wire,  which 
keep  the  solution  reduced. 

Process  of  Analysis. — Fill  all  the  reagent  bulbs  to  the  mark 
on  the  capillary  tubes  by  opening  the  proper  stop-cocks  and 
lowering  the  pressure  bottle  carefully  till  the  liquid  rises  to  the 
right  point.  Do  this  with  one  bulb  at  a  time,  and  on  no  account 
try  to  set  the  level  of  the  liquid  by  opening  or  closing  the  stop- 
cocks. Bring  it  to  the  right  point  by  raising  or  lowering  the 
pressure  bottle,  and  then  close  the  stop-cock.  Proceeding  in 
this  way,  the  fluid  will  never  be  drawn  up  into  the  stop-cock. 
Should  such  an  accident  happen,  the  stop-cock  must  be  immedi- 
ately taken  out,  washed,  and  then  relubricated  with  vaseline. 
The  alkaline  liquid,  if  allowed  to  remain  in  the  glass  stop-cock, 
would  soon  cause  it  to  stick  hopelessly.  Now  set  the  three- 
way  cock  so  that  the  opening  to  the  side  is  connected  with  the 
measuring  tube.  Raise  the  pressure  bottle  till  the  liquid  fills 
the  tube  to  the  mark  on  the  capillary.  Turn  the  cock  so  as  to 
close  this  connection  and  open  the  one  to  the  sample  inlet  tube, 
lower  the  bottle  and  draw  in  slowly  50  or  60  c.c.  of  gas.  This 
should  be  enough  to  completely  wash  out  air  in  the  connecting 
tubes.  Again  reverse  the  stop-cock,  lift  the  bottle  and  run  this 
gas,  which  is  contaminated  with  that  left  in  the  connections  and 
capillaries,  out  through  the  side  tube.  Now  again  reverse  the 
stop-cock  and  draw  in  the  sample  of  gas  for  analysis,  lowering 
the  bottle  until  the  gas  fills  the  measuring  tube  to  some  distance 
below  the  zero  mark.  Close  the  cock  and  set  the  pressure 
bottle  on  a  support  a  little  above  the  level  of  the  zero  point. 
Pinch  the  rubber  near  the  bottom  of  the.  burette,  open  the  cock 
to  the  side  and  carefully  let  the  liquid  run  in  by  releasing  the 
pressure  of  the  fingers  until  it  reads  exactly  zero  on  the  tube. 
Now  close  the  cock  carefully,  take  down  the  bottle,  and  read  the 
volume  of  the  gas  after  equalizing  the  pressure  by  bringing  the 
surface  of  the  liquid  in  the  bottle  to  the  level  of  that  in  the  tube. 
The  reading  should  be  exactly  zero.  If  it  is  0.1  or  0.2  c.c.  off, 
this  can  be  corrected  by  raising  or  lowering  the  level  of  the  water 
in  the  pressure  bottle  until  the  reading  is  zero,  and  making  all 

18 


274  METALLURGICAL  ANALYSIS 

subsequent  readings  in  the   analysis   after  giving  the  leveling 
bottle  the  same  relative  elevation. 

The  measuring  tube  now  contains  100  c.c.  of  gas.  Open  the 
stop-cock  into  the  potash  bulbs  and  run  the  gas  over  by  raising 
the  pressure  bottle.  Be  careful  to  so  hold  the  bottle  that  the 
liquid  will  rise  only  to  the  mark  in  the  gas  tube.  Now  draw  the 
gas  back  in  the  same  way,  run  it  over  again  and  again  back. 
Bring  the  potash  solution  carefully  to  the  mark  in  its  tube,  close 
the  stop-cock,  wait  at  least  30  seconds  for  the  liquid  to  drain 
down  the  side,  level  as  before  and  read  the  volume.  Transfer 
a  second  time  to  the  potash,  draw  it  back  and  read  the  volume 
again.  If  it  does  not  agree  with  the  first  reading,  run  it  over  a 
third  time.  With  fresh  potash  solution,  the  second  reading 
should  always  check  the  first.  The  decrease  in  volume  is  the 
CO2.  Now  proceed  in  the  same  way  with  the  other  tubes,  using 
the  pyrogallic  solution  first  and  then  the  cuprous  chloride.  With 
the  pyrogallate  tube,  the  gas  should  be  run  over  two  or  three 
times  rapidly  before  taking  a  reading,  so  that  the  dark  saturated 
solution  forming  on  the  walls  of  the  bulb  may  not  remain  long  in 
contact  with  the  gas,  as  this  might  lead  to  the  formation  of  CO. 
The  liquid  draining  down  the  side  of  the  bulb  will  show  by  its 
change  of  color  when  it  is  absorbing  oxygen.  As  soon  as  the 
oxygen  is  all  absorbed,  the  liquid  on  the  sides  of  the  bulb  will 
not  turn  brown  as  the  gas  reaches  it.  Always  get  two  readings 
that  agree  before  proceeding  to  the  next  tube.  The  correspond- 
ing decreases  in  volume  give  the  oxygen  and  the  CO.  The  resid- 
ual gas  is  estimated  as  N2.  It  will  contain  any  H2  and  CH4 
present  in  the  original  gas,  but  these  are  rarely  present  in  chimney 
gases  in  measurable  amounts.  When  the  analysis  is  finished, 
run  out  the  residual  nitrogen,  leaving  the  measuring  tube  full 
of  water.  Now  everything  is  ready  for  the  next  test. 

Extreme  care  should  be  taken  to  avoid  getting  any  of  the  absorption 
solutions  into  the  connection  or  measuring  tubes.  Should  this  happen, 
they  must  be  washed  out  and  the  water  in  the  pressure  bottle  changed 
before  starting  a  new  analysis,  as  gas  might  be  absorbed  in  filling  the 
apparatus.  The  Orsat's  apparatus  may  be  used  for  the  determination 
of  C02  and  CO  in  the  gas  from  the  iron  blast  furnace.  In  this  case 
the  residual  gas  invariably  contains  hydrogen  and  methane  and  should 
be  kept  for  further  analysis. 


THE  ANALYSIS  OF  GASES  275 

If  the  pipettes  are  of  the  ''bubbling"  type,  the  absorption  is  more 
rapid. 

BLAST  FURNACE  AND  PRODUCER  GAS 

These  two  gases  are  analyzed  in  the  same  way.  The  writer  prefers 
the  Hempel  apparatus  for  the  analysis  of  these  gases  rather  than  special 
built  up  apparatus,  because  the  Hempel  is  more  convenient  and  is  accu- 
rate. It  is  the  writer's  experience  that  results  with  the  Hempel  appa- 
ratus can  with  care  be  made  accurate  to  0.05  per  cent.  When  greater 
accuracy  than  this  is  desired  it  is  necessary  to  use  some  form  of  apparatus 
such  as  the  one  evolved  by  Mr.  Burrell  of  the  Bureau  of  Mines  and  shown 
on  page  291,  or  such  as  the  Haldane  apparatus.  The  complete  analysis 
of  a  producer  gas  can  be  made  in  less  than  a  half  hour.  What  was  said 
concerning  sampling  and  storage  of  gas  at  the  beginning  of  this  chapter 
applies  here.  If  the  sample  is  taken  over  water,  as  when  a  long  time 
sample  is  taken,  the  surface  of  the  water  must  be  covered  with  paraffin 
shavings. 

Apparatus  Used. — A  is  a  single  pipette  containing  30  per  cent, 
solution  of  KOH  used  for  absorbing  CO2.  B  is  a  pipette  filled 
with  fuming  sulfuric  acid.  The  small  upper  bulb  is  filled  with 
glass  beads  in  order  to  give  a  larger  surface  of  contact  between 
the  gas  and  the  acid.  This  is  used  for  absorbing  the  "illumi- 
nants"  or  unsaturated  hydrocarbons  such  as  ethylene,  C2H4, 
propylene,  C3H6,  etc.  C  is  a  double  pipette  containing  alkaline 
pyrogallate  for  oxygen.  D  D,  double  pipettes  containing  am- 
moniacal  cuprous  chloride,  are  precisely  the  same  as  C.  It  is  not 
necessary  to  use  both  on  gases  containing  but  traces  of  CO  but 
if  the  gases  are  blast-furnace  gas,  or  producer  gas,  or  coke-oven 
gas,  or  water  gas  it  is  necessary  to  use  two  cuprous  chloride 
pipettes  and  even  three  are  sometimes  used.  E  is  a  combustion 
pipette  containing  a  platinum  spiral  which  can  be  heated  with  an 
electric  current.  It  is  made  from  a  single  pipette  for  solid 
reagents.  One  bulb  has  been  cut  off  and  used  for  the  leveling 
bulb.  A  capillary  tube  with  a  stop-cock  is  attached.  The  pi- 
pette is  filled  with  mercury  and  connected  to  a  leveling  bulb  with 
heavy  rubber  tubing.  The  combustion  pipette  sets  in  a  basin  to 
catch  the  mercury  should  the  tube  break.  F  is  the  burette  con- 
nected with  a  leveling  bottle  G.  The  burette  must  be  water 
jacketed  and  a  thermometer  should  hang  in  the  water  of  the 
jacket.  It  is  convenient  to  have  the  stop-cock  a  three-way  one 


276 


METALLURGICAL  ANALYSIS 


but  not  necessary.     H  is  a  capillary  tube  with  an  internal  diame- 
ter between  0.5  and  1.0  mm.  or  about  J4o  m- 

The  rubber  tubes  on  the  pipettes  should  be  made  of  thick- 
walled  pure  gum  and  should  be  wired  to  the  pipettes  by  passing 
the  wire  around  twice  or  more  to  prevent  leakage.  The  rubber 


tube  should  project  beyond  the  end  of  the  capillary  of  the  pipette 
about  1  JfJ  in.  but  not  so  long  but  that  the  air  in  the  tube  can  be 
driven  out  by  squeezing  it  between  the  thumb  and  forefinger. 
Also,  and  this  is  important,  the  tube  should  have  a  band  of  elas- 
tic rubber  about  it  as  shown  in  the  cuts,  in  order  to  make  a  tight 


THE  ANALYSIS  OF  GASES  277 

connection  when  the  capillary  on  the  burette  is  pushed  in  the 
tube.  This  band  is  put  on  as  follows:  Cut  a  piece  of  pure  gum 
tubing  a  little  smaller  in  diameter  than  the  rubber  tube  on  the 
pipette  and  about  a  quarter  of  an  inch  long.  Push  this  on  a 
tapering  glass  tube  (P,  Fig.  21)  until  it  is  at  the  big  end,  which 
should  be  as  large  in  internal  diameter  as  the  rubber  tube  on  the 
pipette.  Push  the  rubber  tube  into  the  glass  tube  about  Y±  in. 
and  then  push  the  rubber  band  off  the  glass  tube  onto  the  rubber 
tube.  This  will  make  the  burette  capillary  fit  in  the  rubber 
tube  without  leaking  gas  and  without  the  bother  of  tying  the 
connection  each  time. 

Filling  the  Pipettes. — To  fill  the  single  pipettes,  simply  pour 
the  reagent  in  the  large  tube  L  until  there  is  enough  to  fill  the 
bulb  M  and  to  have  about  J£  in.  of  the  reagent  in  the  other  bulb. 

To  fill  the  double  pipettes,  first  .pass  an  oxygen  and  carbon 
monoxide  free  gas,  such  as  natural  gas  or  hydrogen,  through  the 
pipettes  until  the  air  is  displaced.  Then  attach  to  the  capillary 
of  the  pipette  a  rubber  tube  the  end  of  which  dips  into  the  re- 
agent which  is  to  be  put  in  the  pipette,  then  suck  on  the  other  end 
of  the  pipette  until  enough  of  the  reagent  has  entered  .to  fill  the 
first  bulb  full  and  about  K  in.  in  the  second.  A  little  experience 
makes  this  easy.  Then  pour  into  the  rear  bulb  125  c.c.  of  water 
to  act  as  a  water  seal  to  keep  out  the  air.  The  purpose  of  filling 
the  bulbs  with  a  neutral  gas  is  to  prevent  the  weakening  of  the 
reagent  by  air  in  the  bulbs. 

The  reagents  are  prepared  as  directed  on  page  271  et  seq. 

Process  of  Analysis. — First  see  that  the  water  in  the  burette 
jacket  is  at  the  same  temperature  as  that  in  the  leveling  bottle. 
The  water  in  the  leveling  bottle  should  be  shaken  with  some  gas 
similar  to  that  to  be  analyzed  and  so  should  the  absorption  solu- 
tions in  the  pipettes  in  order  to  saturate  the  liquids  with  the  gas 
other  than  the  constituent  to  be  absorbed  in  the  solution.  This 
is  most  readily  done  by  making  a  preliminary  analysis  of  the  gas. 
Then  see  that  the  burette  is  tight  by  taking  a  reading,  then  raising 
or  lowering  the  pressure  bottle  and  allowing  the  gas  to  stand 
under  a  pressure  or  vacuum  for  several  minutes.  Then  take 
another  reading.  The  readings  ought  to  agree  exactly.  In 
reading  the  burette  hold  a  finger  or  piece  of  paper  back  of  the 
burette  and  a  little  below  the  meniscus  so  as  to  illuminate  the 


278  METALLURGICAL  ANALYSIS 

bottom  of  the  meniscus  and  make  the  reading  sharp.  With  care 
one  can  be  sure  of  the  reading  to  within  less  than  0.05  c.c.  The 
water  in  the  pressure  bottle  should  contain  about  0.5  per  cent. 
H2S04. 

Now  raise  the  pressure  bottle  until  all  gas  is  out  of  the  burette 
and  water  drops  from  the  end  of  the  capillary.  Also  wash  the 
capillary  by  dipping  the  end  of  it  in  acidulated  water  to  remove 
all  alkali.  Then  attach  the  rubber  tube  of  the  vessel  containing 
the  sample  to  the  burette  capillary,  first  taking  care  to  drive  all 
air  out  of  the  rubber  tube.  Then  lower  the  pressure  bottle  of 
the  burette  and  raise  the  pressure  bottle  of  the  vessel  containing 
the  sample  and  open  the  stop-cock  on  the  burette  and  draw  in 
the  gas  until  a  little  more  than  100  c.c.  has  been  drawn  in.  Close 
the  stop-cock  and  detach  the  sample  vessel.  Allow  the  burette 
to  drain  about  30  seconds.  Raise  the  pressure  bottle  until  the 
bottom  of  the  meniscus  is  just  on  the  zero  (or  100  c.c.)  mark, 
pinch  the  rubber  tube  connecting  the  burette  and  bottle  and  open 
the  stop-cock  momentarily  to  put  the  gas  under  atmospheric 
pressure.  Close  the  cock  and  level  the  water  in  the  burette  ex- 
actly with  the  water  in  the  bottle  and  take  the  reading.  It 
should  read  exactly  zero  (or  100  c.c.).  At  the  same  time  read  the 
temperature  of  the  jacket  water. 

Now  attach  the  KOH  pipette  to  the  capillary  of  the  burette 
as  follows:  squeeze  the  rubber  tube  on  the  pipette  between  the 
thumb  and  forefinger  so  that  all  air  will  be  driven  out  of  the  tube 
and  the  KOH  will  fill  the  capillary  of  the  pipette.  Then  push 
the  capillary  of  the  burette  into  the  rubber  tube  in  such  a  way 
as  not  to  drive  air  into  the  tube  and  until  the  ends  of  the  capil- 
laries are  in  contact.  The  KOH  should  extend  nearly  to  the 
top  of  the  pipette  capillary.  Make  a  mental  note  of  its  position. 
Now  open  the  stop-cock  and  raise  the  pressure  bottle  and  drive 
all  the  gas  over  into  the  pipette.  Close  the  cock  and  shake  the 
KOH  pipette  vigorously  for  20  or  30  seconds,  then  raise  the  pres- 
sure bottle  and  run  a  few  drops  of  water  into  the  pipette  to  wash 
all  KOH  which  was  splashed  into  it  out  of  the  capillary.  Then 
lower  the  pressure  bottle  and  draw  the  gas  back  into  the  burette 
until  the  KOH  rises  in  the  capillary  of  the  pipette  exactly  to  the 
same  height  as  it  was  at  the  beginning.  Allow  the  burette  to 
drain  as  long  as  before  and  take  the  reading  of  the  burette  care- 


THE  ANALYSIS  OF  GASES  279 

fully,  also  read  the  temperature  of  the  jacket.  The  decrease  in 
volume  (if  there  has  been  no  temperature  change)  is  the  percent- 
age of  CO2  in  the  gas.  To  make  sure  that  the  CO2  is  all  absorbed 
repeat  the  above  operation.  The  reading  should  be  the  same  as 
before.  If  not,  run  a  blank  determination  by  again  repeating 
the  operation  of  driving  the  gas  into  the  KOH  pipette,  etc.,  and 
again  read  the  burette  after  the  usual  draining.  If  there  is  a 
further  change  of  volume,  either  positive  or  negative,  it  shows 
that  there  is  a  leak  or  that  the  temperature  is -changing.  Twice 
this  change  in  volume  should  be  added  to  or  subtracted  from  the 
second  reading.  By  taking  this  trouble  of  running  a  blank  the 
results  can  be  relied  upon  to  0.05  per  cent.  For  most  technical 
work  such  care  is  not  necessary  but  should  be  taken  occasionally 
to  check  up  the  work. 

Now  remove  the  KOH  pipette  and  attach  the  fuming  sulfuric 
acid  pipette  in  the  same  way,  making  mental  note  of  the  position 
of  the  acid  in  the  capillary.  The  connection  must  be  especially 
tight  as  it  requires  considerable  pressure  to  drive  the  gas  into 
this  pipette.  Raise  the  pressure  bottle  and  drive  the  gas  into 
the  burette  but  do  not  let  any  water  get  into  the  sulfuric  acid  pipette. 
Pass  the  gas  back  and  forth  between  the  burette  and  pipette 
three  times,  then  bring  the  sulfuric  acid  back  to  the  original  place 
on  the  capillary.  The  gas  now  has  sulfuric  acid  vapors  in  it 
which  must  be  removed  by  passing  the  gas  into  the  KOH  pipette 
and  shaking  vigorously.  Finally  bring  the  gas  back  into  the  bu- 
rette and  read  the  change  in  volume  and  temperature.  If  there 
has  been  no  temperature  change,  the  decrease  in  volume  is  the 
percentage  of  "illuminants,"  chiefly  C2H4.  The  C2H4  is  changed 
into  ethienic  acid,  C2H6S2O7.  Any  acetylene  is  changed  to 
C2H4SO4  and  benzene  to  CeHeSOs.  Since  blast-furnace  gas  con- 
tains no  heavy  hydrocarbons  the  fuming  sulfuric  acid  is  not  used 
when  blast-furnace  gas  is  analyzed. 

It  is  well  to  run  a  blank  on  this  determination  occasionally. 

Next  attach  the  pyrogallate  pipette  and  manipulate  just  as 
with  the  KOH  pipette  except  that  the  shaking  of  the  gas  in  con- 
tact with  the  solution  should  be  much  longer.  The  decrease  in 
volume  is  the  percentage  of  oxygen.  To  make  certain  of  com- 
plete absorption  of  the  oxygen  it  is  necessary  to  run  the  gas  into 
the  pipette  again.  There  should  be  no  change  in  volume. 


280  METALLURGICAL  ANALYSIS 

Next  attach  the  ammoniacal  cuprous  chloride  pipette  and 
manipulate  as  with  the  pyrogallate  pipette.  The  CO  is  absorbed 
slowly  and  the  pipette  should  be  shaken  at  least  100  times,  and  if 
the  cuprous  chloride  has  been  used  before,  the  gas  must  be  run 
into  a  second  cuprous  chloride  pipette  and  shaken  100  times. 
This  is  always  the  best  way  if  the  gas  contains  more  than  2  per 
cent,  of  CO.  When  the  first  pipette  gets  too  slow  in  its  action,  it 
is  emptied  and  filled  with  fresh  solution  and  used  as  the  second 
pipette  while  the  other  one  is  used  first. 

The  gas  now  has  left  in  it  only  hydrogen,  methane,  and 
nitrogen. 

The  hydrogen  and  methane  are  determined  by  combustion  in 
the  combustion  pipette.  They  may  be  determined  by  explosion 
in  an  explosion  pipette  but  the  writer  does  not  like  the  explosion 
method.  The  combustion  method  is  carried  out  as  follows: 
Attach  the  combustion  pipette  to  the  capillary  of  a  burette  con- 
taining oxygen  and  run  in  enough  oxygen  to  uncover  the  platinum 
wire  and  its  connections,  but  do  not  use  more  than  40  c.c.  Meas- 
ure the  oxygen  carefully  and  the  temperature  of  the  burette  from 
which  it  was  taken.  Close  the  stop-cock  of  the  pipette  and  attach 
it  to  the  capillary  of  the  burette  containing  the  gas.  Connect  the 
wires  from  a  source  of  electricity  to  the  terminals  of  the  wires  of 
the  combustion  pipette.  Turn  on  the  current  until  the  plati- 
num wire  in  the  pipette  is  at  a  dull  yellow  of  nearly  the  same 
brightness  as  an  ordinary  incandescent  light  carbon  filament. 
Record  the  temperature  of  the  gas,  then  open  the  stop-cocks  on 
the  burette  and  the  pipette  and  run  the  gas  into  the  pipette  slowly, 
in  order,  in  the  case  of  producer  gas,  to  prevent  an  explosion  or 
melting  of  the  platinum.  The  mercury  in  the  leveling  bulb  of  the 
pipette  should  be  at  about  the  same  level  as  the  mercury  in  the 
pipette  in  order  to  avoid  leaks  due  to  the  great  pressure  caused  by 
considerable  difference  in  levels  of  the  mercury.  After  the  gas  is 
all  in  the  pipette,  close  the  pipette  stop-cock  and  continue  the 
combustion  for  several  minutes.  The  pipette  should  be  kept  cool 
during  the  combustion  by  water  dripping  on  the  cotton,  N  Fig.  21, 
around  the  top.  Now  shut  off  the  electric  current  and  run  the 
residual  gas  back  into  the  burette.  Allow  the  gas  to  cool  a  min- 
ute and  then  read  the  volume  and  temperature.  If  there  has  been 
any  change  in  temperature  make  the  proper  correction.  Call  the 


THE  ANALYSIS  OF  GASES  281 

contraction  in  volume  C.  Now  attach  the  burette  to  the  KOH 
pipette  and  determine  the  CO2  produced  by  the  burning  of  the 
CH4.  The  methane  in  the  gas  was  the  same  in  volume  as  the 
CO2  produced  by  its  combustion,  and  since  the  original  sample 
was  100  c.c.  the  volume  of  C02  produced  in  cubic  centimeters  is 
the  percentage  of  methane  in  the  gas  sample.  The  contraction 
in  volume  due  to  the  burning  of  the  methane  is  twice  the  volume 
of  the  methane,  and  this  contraction  subtracted  from  the  total 
contraction  C  on  burning  gives  the  contraction  due  to  the  burning 
of  the  hydrogen,  which  multiplied  by  %  gives  the  volume  and 
percentage  of  the  hydrogen. 

The  reactions  are:  CH4  (1  vol.)+202  (2  vol.)=C02(l  vol.)  + 
2H2O.  Since  the  H2O  condenses,  the  contraction  is  twice  the 
CH4. 

2H2(2  vol.)+O2  =  2H2O.  Since  the  H2O  condenses,  the 
hydrogen  is  equal  to  two-thirds  of  the  contraction  when  it  is 
burned. 

The  total  time  required  for  the  analysis  of  the  gas  is  about  25 
minutes. 

Notes  on  the  Process. — The  two  cuprous  chloride  pipettes  may  be 
permanently  connected  by  means  of  a  T  capillary,  with  a  stop-cock  in 
each  branch  going  to  a  pipette,  and  the  third  branch  connected  to 
the  burette.  In  this  way  only  one  operation  of  connecting  the  cuprous 
chloride  pipettes  to  the  burette  is  necessary,  although  each  pipette 
works  separately. 

If  the  stop-cock  on  the  burette  is  a  "two-way"  one  it  is  convenient 
to  attach  the  KOH  pipette  permanently  to  one  of  the  ways  because  the 
KOH  pipette  is  used  three  times  during  the  analysis,  and  a  permanent 
attachment  of  it  saves  the  time  of  three  operations.  This  idea  has 
been  carried  out  to  the  extent  of  having  a  stop-cock  with  enough 
different  "ways"  to  have  a  permanent  attachment  for  each  pipette. 

After  each  time  that  a  pipette  is  connected  to  the  burette  a  drop  of 
water  should  be  placed  on  the  top  of  the  rubber  connection,  so  that  if 
the  connection  is  leaking  the  bubbling  of  gas  through  the  drop  may  be 
seen. 

The  combustion  pipette  should  hold  about  150  c.c.  The  platinum 
wire  should  be  inserted  far  enough  in  so  that  40  c.c.  of  gas  in  the  pipette 
will  uncover  the  wire  and  prevent  the  mercury  from  short-circuiting 
the  current.  It  is  best  to  wrap  the  top  of  the  pipette  with  cotton 
and  keep  water  dripping  on  the  cotton  during  the  combustion  so  that 


282  METALLURGICAL  ANALYSIS 

the  glass  will  not  get  so  hot  that  it  is  liable  to  crack.  The  pipette 
must  be  surrounded  with  a  wire  netting  or  gauze  so  that  the  eyes  of 
the  operator  will  be  protected  if  an  explosion  should  take  place.  It 
is  convenient  to  have  a  stop-cock  on  the  combustion  pipette,  but  is  not 
necessary.  If  a  stop-cock  is  not  used,  it  is  necessary  to  close  the  rubber 
tube  on  the  capillary  with  a  glass  plug  when  the  pipette  is  moved  from 
the  oxygen  burette  to  the  burette  containing  the  gas. 

The  electric  connections  for  the  platinum  wire  are  easily  made  as 
follows:  To  the  end  of  a  copper  wire  about  6  in.  long  fasten  a  piece 
of  platinum  wire  of  20  gage  and  1  in.  long  and  pass  it  through  a  piece 
of  glass  tubing  5  in.  long  and  y±  in.  internal  diameter.  Inside  this 
tube  pass  a  smaller  glass  tube  with  another  copper  wire  with  plati- 
num end.  The  platinum  wires  should  project  %  in.  beyond  the  end  of 
the  larger  glass  tube  which  should  be  1  in.  longer  than  the  other.  Now 
heat  the  large  glass  tube  so  that  the  glass  will  soften  and  the  end  will 
close  about  the  platinum  wires.  It  is  well  to  squeeze  the  softened  glass 
with  a  pair  of  pliers  to  close  the  ends  perfectly  and  to  leave  no 
thick  ball  of  solid  glass  which  is  apt  to  crack  when  heated.  The  other 
end  of  the  outer  tube  should  be  constricted  so  that  the  inner  tube  will 
not  fall  out.  Pass  the  tubes  through  a  hole  in  a  rubber  stopper  which 
fits  the  opening  in  the  bottom  of  the  combustion  pipette.  Connect 
the  platinum  ends  with  a  30-gage  platinum  wire,  about  1>^  in.  long  and 
coiled  in  several  coils.  The  platinum  coil  should  be  about  %  in.  from 
the  top  of  the  pipette.  It  is  best  to  provide  a  second  platinum  coil  in  the 
pipette,  connecting  it  to  one  of  the  terminals  above  described  and  to  an 
iron  rod  passing  through  the  mercury  and  the  stopper.  Then  if  one  coil 
melts,  the  other  can  be  used. 

The  platinum  wire  must  be  heated  to  a  dull  yellow  or  the  combus- 
tion is  likely  to  be  incomplete.  The  wire  may  be  heated  by  about 
three  or  four  dry  cells  or  better  by  the  current  through  six  16-candle- 
power  electric  lights  placed  in  parallel  on  a  110-volt  circuit.  That  is, 
a  current  of  about  3  amperes  is  required,  depending,  of  course,  on  the 
diameter  of  the  wire.  If  the  wire  is  heated  hotter  than  a  dull  yellow 
a  slight  error  is  caused  due  to  formation  of  N2O4. 

When  a  gas  contains  ethane  as  well  as  methane  and  hydrogen,  which 
is  not  the  case  with  producer  or  blast-furnace  gas,  the  hydrogen  must  be 
determined  separately  as  directed  under  the  analysis  of  coke-oven  gas. 
Of  course  the  hydrogen  in  producer  or  blast-furnace  gas  may  be  de- 
termined separately,  but  this  is  not  necessary.  If  the  gas  contains 
hydrogen  and  no  methane  the  combustion  pipette  may  be  filled  with 
water  instead  of  mercury.  Blast-furnace  gas  contains  only  about  0.2 
per  cent,  methane.  If  the  gas  contains  both  hydrogen  and  methane 
and  the  hydrogen  is  removed  first,  the  combustion  of  methane  may 
be  made  without  mercury. 


THE  ANALYSIS  OF  GASES  283 

Gas  Analysis  without  use  of  Cuprous  Chloride.  —  Instead  of  absorbing 
the  CO  in  cuprous  chloride  and  then  determining  the  hydrogen  and 
methane  by  combustion,  the  carbon  monoxide,  hydrogen  and  methane 
may  be  all  determined  together  by  combustion  without  having  to  use 
the  cuprous  chloride.  This  applies  only  to  gases  like  producer  and  blast- 
furnace gases  which  have  no  hydrocarbons  higher  than  methane. 

Process  of  Analysis.  —  Carry  out  the  combustion  exactly  as 
above  directed.  Measure  the  decrease  in  volume  after  combus- 
tion, and  then  determine  the  CO2  produced  by  the  combustion  by 
passing  the  residue  into  the  KOH  pipette.  Then  determine  the 
amount  of  oxygen  left  after  the  combustion  by  absorbing  it  in 
pyro  solution.  Also  carefully  determine  the  amount  of  oxygen 
in  the  volume  of  oxygen  used  by  passing  the  same  volume  of 
oxygen  through  the  pyrogallate  pipette.  The  difference  between 
the  two  gives  the  amount  of  oxygen  used.  Calculate  the  results 
as  follows  :  The  reactions  of  combustion  are  as  given  above  for 
hydrogen  and  methane  and  as  follows  for  carbon  monoxide: 
2CO  (2  vol.)+02(l  vol.)  =2C02(2  vol.).  Let  x  =  hydrogen,  y  = 
methane  and  z  =  carbon  monoxide.  Then  we  have  the  fol- 
lowing equations: 

Contraction  during  combustion  =  %x+2y4-  }^z. 
Carbon  dioxide  produced  y-fz. 

Oxygen  consumed  =  J 


Combining  these  equations  we  get  the  relations: 

Hydrogen  =  contraction  minus  oxygen  consumed. 

Methane  =  oxygen  consumed  minus  ^  contraction  minus  % 
CO2  produced. 

Carbon  monoxide  =  %  CO2  produced  plus  J£  contraction 
minus  oxygen  consumed. 

Notes  on  the  Process.  —  This  method  requires  less  time  for  manipula- 
tion but  more  time  for  calculation  than  the  one  previously  given.  They 
are  about  equally  accurate. 

There  is  a  correction  necessary  for  accurate  work  when  a  gas  is 
burned  which  gives  a  large  amount  of  C02.  It  is  due  to  the  fact  that 
the  molecular  volume  of  CO2  is  22.26  liters  while  that  of  CH4  is  22.44 
liters  and  of  CO  is  22.39  liters.  That  is,  the  C02  produced  by  burning 
100  c.c.  of  methane  is  99.20  c.c.  instead  of  100  c.c.,  because  CO2  departs 
considerably  from  being  a  perfect  gas.  So  that  when  CO  or  CH4 


284  METALLURGICAL  ANALYXIH 

are  burned,  the  contraction  in  volume  should  be  corrected  by  subtracting 
from  it  0.8  per  cent,  of  the  volume  of  C02  produced  and  the  volume 
of  the  C02  should  be  increased  by  0.8  per  cent,  of  the  measured  amount 
of  C02  in  order  to  calculate  the  volume  of  the  methane  or  the  CO. 

The  determination  of  dust  in  unwashed  blast-furnace  gas  is  an 
exceedingly  difficult  proposition.  For  the  apparatus  and  details  used 
for  this  determination  see  TOUZALIN  and  BRADY,  Jour.  Ind.  Eng.  Chem., 
Ill,  pp.  662-670. 

THE  COPPER  OXIDE  METHOD 

The  methods  described  above  are,  in  the  author's  opinion,  very  re- 
liable and  accurate.  However,  H.  H.  Worrell  recommends  Jiiger's 
method  modified.  (See  Met.  Chem.  Eng.,  XI,  245.)  In  outline  it  is 
as  follows:  Analyze  the  gas  just  as  above  described  until  the  oxygen 
is  removed.  Then  connect  between  the  burette  and  a  single  Hempel 
pipette  filled  with  acidified  water,  or,  better,  with  mercury,  a  silica  tube, 
Y±  in.  bore  by  7  in.  long.  This  tube  is  filled  with  copper  oxide  and  sur- 
rounded with  an  air  bath  (Eimer  and  Amend  catalogue  No.  2073). 
The  air  bath  is  then  brought  to  250°C.  and  the  gas  in  the  burette  is 
slowly  passed  through  the  tube  and  back  again  until  the  hydrogen  is  all 
burned  which  will  require  6  to  8  passes.  Cool  the  tube,  return  the  gas 
to  the  burette  so  that  the  water  in  the  pipette  is  at  the  original  level  in 
the  capillary  and  read  the  contraction  in  volume.  The  contraction  is 
the  volume  of  the  hydrogen  present  in  the  gas  plus  the  oxygen  that  was 
in  the  tube.  Then  pass  the  gas  into  a  KOH  pipette  and  determine 
the  C02  formed  by  the  oxidation  of  the  CO.  The  volume  of  CO2 
found  is  the  same  as  the  volume  of  CO  that  is  present  in  the  gas. 

Now  heat  the  silica  tube  to  redness  and  pass  the  gas  back  and  forth 
until  the  hydrocarbons  are  all  oxidized.  Cool  and  measure  the  vol- 
ume. If  an  increase  in  volume  is  observed  it  is  due  to  ethane  and  is 
equal  to  the  ethane  present.  Then  pass  the  gas  into  the  KOH  pipette 
and  measure  the  C02  absorbed.  The  C02  found  minus  twice  the  vol- 
ume of  the  ethane  is  equal  to  the  methane. 

The  amount  of  air  held  by  the  silica  tube  can  be  found  once  for  all 
for  the  correction  of  the  hydrogen  determination,  but  it  is  better  to  fill 
the  tube  with  nitrogen.  The  copper  oxide  must  be  reoxidized  after  a 
determination  by  drawing  air  through  the  hot  tube. 

The  Analysis  of  Coke-oven  Gas. — Up  to  the  combustion  the 
analysis  of  this  gas  is  carried  on  in  exactly  the  same  manner  as 
for  producer  gas,  except  for  the  following:  Since  coke-oven  gas 
has  a  rather  large  amount  of  "heavy  hydrocarbons"  the  absorp- 


THE  ANALYSIS  OF  GASES  285 

tion  of  them  in  the  fuming  sulfuric  acid  should  be  given  more 
time.  After  determining  the  "heavy  hydrocarbons"  run  the  gas 
over  into  the  sulfuric  acid  to  see  if  a  further  contraction  is 
obtained.  If  it  is,  more  time  for  the  absorption  must  be  used. 

About  90  to  100  c.c.  of  oxygen  must  be  used  for  the  combustion 
of  the  entire  combustible  residue.  This  is  run  into  the  combus- 
tion pipette  and  then  the  spiral  is  heated  to  a  dull  yellow  and 
the  gas  run  into  the  pipette  very  slowly  in  order  to  prevent  an 
explosion.  It  is  best  to  set  the  pressure  bottle,  attached  to  the 
burette,  up  high  with  a  screw-cock  on  the  rubber  connection 
closed.  Then  open  the  screw-cock  just  enough  so  that  the  gas 
will  all  be  driven  into  the  combustion  pipette  in  about  five  min- 
utes. The  top  of  the  pipette  should  be  kept  cool  as  directed 
under  the  analysis  of  producer  gas.  After  the  gas  is  all  in  the 
pipette  the  spiral  should  be  kept  hot  for  a  few  minutes. 

Coke-oven  gas  may  have  some  ethane  in  it;  coal  gas  is  sure  to  have. 
In  such  a  case  it  is  necessary  to  make  a  separate  determination  of 
hydrogen  by  the  palladiumized  asbestos  method,  for  hydrogen  cannot 
be  determined  when  a  mixture  of  hydrogen,  methane  and  ethane  are 
burned  together.  The  method  is  given  below. 

Determination  of  Hydrogen  by  Combustion  in  Contact  with  Palla- 
dium.— When  a  gas  containing  hydrogen  in  the  presence  of  methane 
and  ethane  is  mixed  with  oxygen  and  passed  over  palladium  heated  to 
90°  to  100°  the  hydrogen  is  completely  burned  to  water  but  the  methane 
and  ethane  are  unaffected  if  the  temperature  is  not  allowed  to  rise  too 
high.  If  the  gas  contains  much  hydrogen  it  should  not  be  passed  over 
the  palladium  so  fast  as  to  cause  the  palladiumized  asbestos  to  glow, 
for  then  some  methane  will  be  oxidized. 

The  palladiumized  asbestos  is  prepared  as  follows:  Dissolve 
1  gram  palladium  in  aqua  regia,  evaporate  the  solution  to  dryness 
on  a  water-bath,  so  as  to  remove  any  adhering  hydrogen  chloride 
as  completely  as  possible,  and  dissolve  the  palladium  chloride 
thus  produced  in  a  very  little  water.  To  this  add  a  few  cubic 
centimeters  of  a  cold  saturated  solution  of  sodium  formate  and 
sufficient  sodium  carbonate  to  produce  a  strongly  alkaline 
reaction.  Now  introduce  1  gram  of  very  soft,  long-fibered 
asbestos,  which,  if  any  excess  of  water  has  been  avoided,  ab- 
sorbs the  whole  liquid  and  forms  with  it  a  thick  paste.  This 
is  dried  at  a  gentle  heat,  by  which  process  black,  finely  divided 


286  METALLURGICAL  ANALYXIH 

palladium  is  uniformly  precipitated  upon  the  asbestos-fiber. 
In  order  to  make  the  palladium  adhere,  the  asbestos  thus  pre- 
pared must  be  heated  on  a  water-bath  till  completely  dry,  then 
soaked  in  a  little  warm  water,  put  into  a  glass  funnel,  and 
freed  from  all  adhering  salts  by  thorough  washing,  without 
removing  any  palladium.  After  drying,  the  substance  exhibits  a 
dark  gray  color,  has  a  slight  tendency  to  stain  the  fingers,  and 
contains  50  per  cent,  palladium.  It  possesses  a  very  high  degree 
of  chemical  activity;  in  the  perfectly  dry  state  it  can  cause  the 
combination  of  hydrogen  and  oxygen  even  at  the  ordinary  tem- 
perature, but  in  order  to  secure  this  result  it  is  always  employed 
in  the  heated  state. 

For  the  preparation  of  the  capillary  combustion  tubes,  employ 
capillary  glass-tubing  of  about  1  mm.  bore  and, 6  mm.  outside 
diameter,  cut  in  pieces  16  or  18  cm.  long  and  bent  as  shown 
at  O,  Fig.  21.  The  asbestos-fiber  must  be  introduced  into  them 
before  bending  off  the  end,  in  the  following  way:  a  few  loose 
fibers  of  the  palladium-asbestos  are  laid  alongside  each  other  on 
smooth  filter-paper  up  to  a  length  of  4  cm. ;  they  are  moistened 
with  a  few  drops  of  water,  and  by  sliding  the  finger  over  them, 
are  twisted  into  a  fine  straight  thread,  which  in  the  moist  state 
has  the  thickness  of  stout  sewing-cotton.  This  thread  is  grasped 
at  one  end  with  the  nippers,  and,  without  bending  or  nicking, 
is  slid  from  above  into  the  capillary  tube,  which  is  held  vertically. 
This  is  then  filled  with  water  by  means  of  the  washing-bottle, 
and  by  jerking  or  by  drawing  off  the  water  the  asbestos-thread 
is  brought  into  the  center  of  the  tube.  This  is  now  allowed 
to  dry  in  a  warm  place.  It  is  well  to  have  small  bulbs  blown 
near  each  end  of  the  tube  to  prevent  films  of  water  getting  to  the 
palladium. 

Procedure  for  the  Determination  of  Hydrogen. — After  the  CO 
has  been  determined  by  absorption  in  cuprous  chloride,  trans- 
fer one-half  of  the  remaining  gas  back  into  the  cuprous  chloride 
pipette,  keeping  the  other  half  in  the  burette.  This  may  con- 
tain as  high  as  30  c.c.  of  hydrogen.  Draw  into  the  burette  15  c.c. 
of  oxygen  and  then  enough  air  to  fill  the  burette  to  100  c.c. 
There  will  now  be  about  twice  as  much  oxygen  present  as  is 
theoretically  necessary  to  burn  the  hydrogen.  Carefully  read 
the  burette  and  its  temperature.  Then  attach  the  palladiumized 


THE  ANALYSIS  OF  CASES  287 

asbestos  capillary,  place  a  small  beaker  of  water  under  it  so  that 
the  capillary  is  immersed,  heat  the  water  to  boiling  and  attach  the 
other  end  of  the  capillary  to  a  Hempel  pipette  containing  only 
acid  water.  Pass  the  gas  through  the  palladium  capillary  at 
the  rate  of  about  15  c.c.  per  minute,  taking  care  that  the  gas 
does  not  pass  through  so  rapidly  that  the  heat  generated  by  the 
burning  hydrogen  causes  the  palladium  to  glow.  Do  not 
allow  the  water  of  the  burette  or  pipette  to  rise  up  to  the  palla- 
dium. When  the  gas  has  all  passed  over,  draw  it  back  into  the 
pipette  and  carefully  read  the  volume  and  temperature.  The 
hydrogen  should  be  all  burned,  but  to  make  sure,  again  pass  the 
gas  over  and  back.  There  should  be  no  change  in  volume  the 
second  time.  The  total  contraction  multiplied  by  %  gives  the 
hydrogen  present  and  this  multiplied  by  2  gives  the  percentage 
of  hydrogen. 

Now  to  see  if  any  methane  has  been  burned  (none  should  have 
been  if  the  palladium  was  not  allowed  to  glow)  pass  the  gas  into 
the  KOH  pipette.  If  any  CO2  is  found  some  methane  was  burned 
and  a  correction  must  be  made. 

Determination  of  the  Methane  (and  Ethane). — Measure  about 
75  c.c.  of  oxygen  and  pass  it  into  the  combustion  pipette.  Heat 
the  platinum  spiral  to  a  bright  yellow  and  carry  out  the  combus- 
tion as  directed  under  the  analysis  of  producer  gas  except  that 
the  combustion  must  be  made  more  carefully  and  slowly  because 
of  the  more  inflammable  nature  of  the  gas.  After  the  combustion, 
determine  the  contraction  in  volume  and  the  CO2  produced. 

From  the  contraction  in  volume  obtained,  subtract  the  con- 
traction due  to  the  burning  of  the  hydrogen.  This  gives  the 
contraction  due  to  the  burning  of  the  methane  and  ethane. 
Then  let  X  =  the  CH4  and  Y  =  the  C2H6.  We  have  the  relations: 

Contraction  =  2X  +  2.5Y 
and  CO2=X  +  2Y 

Solving  we  get 

v  (  4  X  contraction  —  5CO2 

X  (or  methane)  =  -  or  CH4  =  CO2  — 2C2H6 

o 

and 

4CO2  — 2  X  contraction 


Y  (or  ethane)  = 


3 


288  METALLURGICAL  ANALYSIS 

The  reaction  for  the  combustion  of  ethane  is: 
2C2H6  (2  vol.)  +  702  (7  vol.)  =4CO2  (4  vol.)  +  6H2O  (condensed). 

The  results  obtained  for  methane  and  ethane  when  multiplied 
by  two  give  the  percentage  in*  which  they  were  present  in  the 
sample.  The  oxygen  consumed  may  be  determined  to  check 
the  results. 

Notes  on  the  Analysis  of  Coke-oven  Gas. — The  gas  is  apt  to  contain 
some  hydrocarbon  vapors  such  as  C6H6,  etc.  For  their  determination 
see  page  290. 

The  fuming  sulfuric  acid  absorbs  the  olefins,  CnH2n,  acetylene,  C2H2, 
the  benzene  hydrocarbons,  such  as  C6H6  and  the  higher  paraffin  hydro- 
carbons such  as  C5Hi2  and  C6Hi4.  If  it  is  desired  to  know  how  much 
benzene  is  present,  the  total  heavy  hydrocarbons  are  determined  by 
absorption  in  fuming  sulfuric  acid.  Then  in  another  sample  they 
are  absorbed  with  a  standard  bromine  solution.  The  bromine  com- 
bines with  the  ethylene  to  form  C2H4Br2  but  does  not  combine  with  the 
benzene.  The  excess  bromine  is  titrated  with  potassium  iodide  and 
sodium  thiosulfate,  from  which  the  ethylene  can  be  calculated.  (HABER 
and  OECHELHAUSER,  Berichte,  XXIX,  p.  2700.)  At  coke-oven  works 
the  benzene  is  determined  by  passing  the  gas  through  four  absorbing 
bottles  containing  cooled  paraffin  oil,  sp.  gr.  0.89,  boiling-point  360°C. 
The  gas  dried  by  passing  over  CaCl2  is  passed  through  these  bottles 
cooled  by  ice,  the  bottles  connected  by  glass,  not  by  rubber,  until  a 
large  volume  has  passed  through  at  about  2  c.c.  per  second.  The  in- 
crease in  weight  of  the  bottles  gives  the  weight  of  benzene  absorbed. 

Naphthalene  is  determined  by  passing  several  cubic  feet  of  the 
purified  gas  through  a  N/20  picric  acid  solution,  filtering  off  the  naph- 
thalene picrate  and  titrating  the  excess  picric  acid  with  N/5  Ba(OH)2 
using  phenolpthalein  indicator  (see  WHITE,  "Gas  and  Fuel  Analysis.") 

Benzene  is  absorbed  by  water  and  KOH  solution,  therefore  if  the  gas 
contains  benzene  either  the  fuming  sulfuric  acid  must  be  used  before 
the  KOH  or  the  KOH  must  be  saturated  with  benzene.  Alkaline 
pyrogallate  absorbs  a  small  amount  of  the  higher  paraffine  (Bui.  42, 
U.  S.  Bureau  of  Mines). 

Upon  prolonged  contact  fuming  sulfuric  acid  will  absorb  some  methane 
and  ethane.  This,  however,  is  negligible  if  the  time  of  contact  is  not 
prolonged  beyond  5  or  10  minutes.  The  same  is  true  of  bromine. 

According  to  Fritzche  (Z.  f.  angew.  Chem.,  1896,  p.  456)  ethylene  can 
be  separated  from  butylene  by  sulfuric  acid,  sp.  gr.  1.62,  which  dissolves 
butylene  but  not  ethylene. 


THE  ANALYSIS  OF  GASES  289 

Cuprous  chloride  absorbs  ethylene  and  acetylene.  These  gases 
therefore  must  be  removed  before  the  CO.  It  also  slightly  dissolves 
the  higher  paraffins. 

ANALYSIS  OF  NATURAL  GAS 

According  to  the  experience  of  Mr.  Burrell  of  the  Bureau  of  Mines, 
the  natural  gas  of  this  country  does  not  contain  any  unsaturated  hydro- 
carbons, although  a  slight  absorption  is  obtained  with  fuming  sulfuric 
acid  due  to  the  absorption  of  other  hydrocarbons.  Neither  does  the  gas 
contain  carbon  monoxide  or  hydrogen.  These  gases  should  never  be 
reported  as  present  in  natural  gas  unless  a  qualitative  test  is  obtained 
for  them.  The  test  for  unsaturated  hydrocarbons  is  made  as  follows: 
Prepare  a  1  per  cent,  neutral  solution  of  palladous  chloride,  PdCh, 
containing  5  per  cent,  sodium  acetate  and  pass  a  large  volume  of  the 
gas  through  the  solution  after  first  passing  it  through  a  KOH  solution 
to  remove  any  H2S  present.  If  there  is  any  ethylene  in  the  gas  it  will 
reduce  the  palladium  and  a  black  precipitate  of  palladium  will  settle 
out.  Any  CO  will  also  reduce  the  palladium  but  as  it  is  oxidized  to  C02 
its  presence  may  be  detected  bypassing  the  gas  through  Ba(OH)2  after 
passing  through  the  palladous  chloride.  (See  BRUNCK,  Z.  angew, 
Chem.,  25,  2479.)  For  the  blood  test  for  CO  see  page  295. 

Process  of  Analysis. — Draw  into  the  burette  100  c.c.  of  the 
gas  and  absorb  the  CO2  in  KOH  and  the  oxygen  (some  may  have 
leaked  into  the  sample)  in  the  pyro  solution.  Then  run  the  gas 
back  into  the  pipette.  Carefully  measure  about  100  c.c.  of 
oxygen,  take  its  temperature  and  pass  it  into  the  combustion 
pipette.  Then  carefully  draw  just  one-third  of  the  gas  from  the 
pyrogallate  pipette  into  the  burette.  Pass  an  electric  current 
through  the  platinum  spiral  to  heat  it  to  a  yellow  heat  while  the 
top  is  kept  cool  by  water  dripping  on  the  cotton  cap  and  then 
pass  the  gas  into  the  pipette  carefully  so  that  not  more  than  10 
c.c.  passes  in  per  minute.  This  is  best  done  by  entirely  closing 
the  tube  connecting  the  leveling  bottle  with  the  burette  with 
a  screw  cock,  then  setting  the  leveling  bottle  up  high,  then  care- 
fully opening  the  screw  cock  until  the  gas  is  slowly  passing  into 
the  combustion  pipette.  The  mercury  in  the  leveling  bulb  of 
the  pipette  should  be  kept  about  level  with  that  in  the  pipette 
to  prevent  leaks.  These  are  not  likely  to  happen  if  the  rubber 
connections  are  reinforced  by  rubber  bands  as  directed  on  page 
277. 

19 


290  METALLURGICAL  ANALYSIS 

After  the  gas  has  all  passed  over  into  the  pipette,  keep  the 
platinum  spiral  hot  for  several  minutes  to  insure  complete  com- 
bustion. Then  break  the  circuit,  allow  the  gas  to  cool  a  minute 
or  so  and  run  the  gas  back  into  the  burette.  After  proper 
drainage  read  the  volume  of  the  gas  and  its  temperature.  Then 
pass  the  gas  into  the  KOH  pipette  and  determine  the  amount  of 
CC>2  produced  by  the  combustion.  The  methane  and  ethane 
are  calculated  as  directed  on  page  287.  Trifling  amounts  of 
oxides  of  nitrogen  may  be  produced  by  the  combustion. 

In  order  to  check  the  result  another  third  of  the  gas  may  be 
taken  from  the  pyrogallate  pipette  and  the  combustion  repeated. 
It  is  necessary  to  remember  that  the  capillary  of  the  burette  holds 
an  appreciable  volume  and  in  taking  a  fraction  of  a  sample  in 
this  way  this  volume  must  be  taken  into  account.  The  volume 
of  the  capillary  may  be  determined  by  drawing  into  the  burette 
some  air  or  gas,  reading  the  volume,  then  dipping  the  end  of  the 
capillary  under  water  and  drawing  water  into  the  capillary  until 
it  is  filled  and  reading  the  volume  again.  The  difference  is  the 
volume  of  the  capillary. 

The  combustion  pipette  should  be  surrounded  with  a  wire 
screen  to  protect  the  operator  in  case  of  an  explosion. 

It  has  been  assumed  that  the  only  hydrocarbons  present  are 
methane  and  ethane.  There  may  be  higher  hydrocarbons  pres- 
ent. These  are  determined  by  absorbing  them  in  absolute 
alcohol.  Their  solubilities  in  alcohol  are  as  follows: 

1  volume  of  alcohol  dissolves  0.52  volumes  of  CH4  at  0°C. 
1  volume  of  alcohol  dissolves  1.5  volumes  of  C2H6  at  0°C. 
1  volume  of  alcohol  dissolves  6.0  volumes  of  C3H8  at  0°C. 
1  volume  of  alcohol  dissolves  18.0  volumes  of  C4Hi0  at  0°C. 

Pass  into  the  combustion  pipette  or  another  one  filled  with  mer- 
cury 2  c.c.  of  absolute  alcohol  or  1  c.c.  of  kerosene,  then  pass  in 
about  100  c.c.  of  the  gas  in  question  and  shake  it  with  the  gas 
about  a  minute.  This  saturates  the  alcohol  with  methane  and 
ethane.  Run  the  gas  out  of  the  pipette  and  the  alcohol  up  in  the 
capillary  and  then  pass  into  the  pipette  100  c.c.  of  the  carefully 
measured  fresh  gas.  Shake  this  with  the  alcohol  and  then  meas- 
ure the  decrease  in  volume  after  the  gas  has  stood  in  the  burette 
long  enough  for  all  the  alcohol  vapors  to  dissolve  in  the  water. 


THE  ANALYSIS  OF  GASES 


291 


I  a 


The  decrease  in  volume  is  the  amount  of  hydrocarbons  higher 
than  ethane.  If  there  is  a  large  amount  of  these,  one  treatment 
with  alcohol  is  not  enough.  The  writer  has  obtained  good  re- 
sults in  this  way  using  gas  into  which  had  been  introduced 
known  amounts  of  gaso- 
line vapors,  petroleum 
ether  vapors,  and  ben- 
zene vapors. 

The  calorific  values  of 
gases  may  be  very  accu- 
rately calculated  from  the 
analysis  using  the  data  given 
in  the  table  on  page  327, 
remembering  that  the  anal- 
yses of  the  gas  are  always  on 
the  dry  basis  (page  264). 

When  extreme  accuracy 
is  necessary  in  the  anal- 
ysis of  gases  by  the  above 
methods  it  is  necessary  to 
use  somewhat  different  ap- 
paratus, which  always  in- 
volves the  use  of  a  compen- 
sator attached  to  the  bu- 
rette and  the  burette  must 
be  graduated  to  0.01  c.c. 
The  apparatus  shown  in 
Fig.  22  is  the  one  devised 
by  Mr.  George  Burrell  of  the 
Bureau  of  Mines.  For  fur- 
ther particulars  see  J.  Eng. 
Chem.,  Vol.  IV,  No.  4. 


FIG.  22. 


THE  ANALYSIS  OF  MINE  AIR 

This  may  be  done  with  the  above  mentioned  apparatus  of  Burrell 
or  Haldane  or  by  the  use  of  the  Hesse  apparatus  here  described.  The 
results  are  very  accurate. 

The  titration  method  for  mine  air  analysis  is  especially  good  on  ac- 
count of  the  very  large  sample  which  can  be  used  and  the  simplicity  pf 
the  apparatus, 


292 


METALLURGICAL  ANALYSIS 


The  CQz  is  determined  by  absorbing  it  in  a  standard  Ba(OH)2  solution, 
the  excess  of  Ba(OH)2  being  titrated  by  a  standard  oxalic  acid  solution. 

The  methane  is  burned  to  COs  by  means  of  a  yellow  hot  platinum  wire, 
and  the  C02  produced  is  determined  as  above  indicated. 

Solutions  Required. — A  barium  hydroxide  solution  made  by 
dissolving  15  grams  Ba(OH)2  8H2O  and  J^  gram  of  BaCl2  in 

water   and   diluting   to   a  liter. 
The  reaction  with  CO2  is, 

Ba(OH)2+CO2  =  BaC03+H2O. 

One  liter  of  C02  at  0°C.  and 
760  mm.  pressure  weighs  1.965 
grams,  and  the  amount  of 
Ba(OH),2  to  be  dissolved  in  a 
liter  is  calculated  thus,  315.5  : 
44  : :  X  :  1.965.  X  =  14.09.  This 
would  theoretically  require  14.09 
grams  Ba(OH)2.8H2O  in  a  liter 
so  that  1  c.c.  would  equal  1  c.c. 
of  C02  at  0°C.  and  760  mm. 
pressure,  but  the  Ba(OH)2.8H2O 
is  never  pure.  The  BaCl2  is 
added  to  make  the  end  point 
with  phenolphthalein  sharp  by 
decreasing  the  ionization  of 
the  BaC204  formed  during  the 
titration. 

An  oxalic  acid  solution,  1  c.c. 
of  which  equals  1  c.c.  CO2,  is 
used  as  a  standard.  Oxalic  acid 
can  be  obtained  pure,  it  conse- 
quently is  made  of  exactly  the 
right  strength  and  the  Ba(OH)2 

solution  is  standardized  against  it.  The  reaction  is  Ba(OH)2+ 
H2C2O4  =  BaC204+2H2O.  One  molecule  of  oxalic  acid  is  there- 
fore equivalent  to  one  of  CO2  and  the  amount  of  oxalic  acid 
required  in  a  liter  of  solution  so'that  1  c.c.  =  1  c.c.  CO2  is  calcu- 
lated thus  (the  formula  of  crystallized  oxalic  acid  being  H2C2O4 
2H2O)  126,04  :  44  : :  X  :  1.965.  X  =  5.629.  Weigh  this  amount 


FIG.  23. 


THE  ANALYSIS  OF  GA81M  293 

carefully,  dissolve  in  CO2  free  distilled  water  and  dilute  to  a  liter 
with  CO2  free  water. , 

The  Ba(OH)2  solution  should  be  kept  in  a  bottle  arranged  as 
shown  in  Fig.  23.  In  this  way  the  carbon  dioxide  of  the  air  is 
kept  from  the  Ba(OH)2.  The  tube  E  contains  soda  lime. 

The  samples  are  taken  in  strong  Erlenmeyer  flasks  of  from  500 
to  1500  c.c.  capacities  depending  upon  the  amount  of  CO2  and 
CH4  in  the  mine  air.  The  flask  is  calibrated  by  filling  it  with 
distilled  water,  forcing  a  two-holed  stopper  into  it,  wiping  dry 
on  the  outside  and  weighing.  The  flask  is  then  emptied,  dried 
and  weighed  with  the  stopper.  The  difference  divided  by  the 
weight  of  1  c.c.  of  water  at  the  observed  temperature  of  the  water 
is  the  volume  of  the  flask. 

Process  of  Analysis. — Place  in  the  neck  of  the  dry  flask  a  paper 
funnel  made  in  the  shape  of  an  ordinary  glass  funnel,  extending 
nearly  to  the  bottom  of  the  flask.  Swing  the  flask  and  funnel 
with  the  funnel  mouth  turned  against  the  air  in  the  place  where 
the  sample  is  to  be  taken.  The  swinging  should  be  done  100 
times  to  remove  the  air  previously  in  the  flask.  Then  place  the 
two-holed  stopper  in  the  flask  with  plugs  in  the  holes  and  take 
the  sample  to  the  laboratory. 

On  reaching  the  laboratory  remove  the  plugs  and  insert  the 
tip  of  the  Ba(OH)2  burette  which  should  not  fit  tightly  in  the 
hole.  Run  in  10  to  20  c.c.  of  Ba(OH)2  solution,  add  four  drops  of 
phenolphthalein  solution  and  replace  the  plugs.  Shake  the  flask 
frequently,  and,  while  the  CO2  is  being  absorbed,  standardize 
the  Ba(OH)2  solution  by  running  into  a  similar  flask  filled  with 
pure  outdoor  air  the  same  amount  of  Ba(OH)2  solution  as  was 
used  above  and  shake  both  flasks  for  five  minutes,  without 
splashing  up  on  the  stopper.  Then  remove  the  plugs,  insert  the 
tip  of  a  burette  through  the  stopper  and  run  in  standard  oxalic 
acid  until  the  phenolphthalein  just  loses  its  red  color.  Do  this 
to  both  solutions. 

Suppose  that  20  c.c.  of  Ba(OH)2  solution  were  used  in  each  case  and 
that  21  c.c.  of  oxalic  acid  were  required  to  standardize  the  Ba(OH)2. 
Further  suppose  that  15  c.c.  of  oxalic  acid  were  used  to  titrate  the 
Ba(OH)2  left  after  absorption  of  the  CO2  in  the  sample.  Then  we  have 

21  c.c.  oxalic  acid+C02  in  pure  air  =  20  c.c.  Ba(OH)2. 

15  c.c.  oxalic  acid+C02  in  the  sample  =  20  c.c.  Ba(OH)2. 

C02  in  sample  =  6  c.c.  +  COz  in  pure  air. 


294 


M E TA  LL  URGICA  L  A  NA L  Y ,S7 X 


If  the  flasks  had  volumes  of  1000  c.c.  each  and  the  temperature  of 
the  sample  was  20°C.  and  barometric  pressure  was  745  mm.  the  per- 
centage of  C02  in  the  sample  would  be, 

(6+0.3)^(1000-20  c.c.    displaced    by    Ba(OH)2   solution)  X27%93X 
=  0.704. 


Pure  air  contains  0.03  per  cent.  C02. 

While  the  above  determination  of  C02  is  being  made,  the 
methane  is  determined  in  another  flask  whose  volume  has  been 
determined  as  above  directed  with  the  stopper  carrying  the  elec- 
trode in  it  in  the  flask  (Fig.  24).  When 
the  flask  is  brought  to  the  laboratory  the 
stopper  in  it  is  exchanged  under  pure  distilled 
water  for  a  stopper  carrying  the  electrode 
made  as  directed  on  page  282.  The  stopper 
should  also  have  a  hole  with  a  glass  plug.  It 
is  best  to  stopper  the  flask  at  the  place  of 
taking  the  sample  with  the  stopper  having 
the  electrode  in  it,  then  the  exchange  of 
stoppers  is  eliminated. 

Now  place  the  flask  with  the  electrode 
reaching  nearly  to  the  bottom  under  a  stream 
of  water  and  pass  through  the  platinum  wire 
sufficient  electric  current  to  heat  it  yellow  hot 
and  continue  the  heating  at  least  fifteen  minutes.  The  flask 
must  be  kept  cool  or  the  air  in  it  will  expand  and  burst  it.  Now 
turn  off  the  current  and  determine  the  C02  in  the  flask,  in  ex- 
actly the  same  way  as  above  directed.  This  includes  both  the 
CO2  proditced  by  the  burning  of  the  methane  and  the  CO2  already 
in  the  original  sample.  From  this  total  is  subtracted  the  CO2 
found  in  the  same  volume  of  the  other  sample  and  the  difference 
is  the  CO2  produced  by  the  burning  of  the  methane,  which  is 
the  same  as  the  volume  of  the  methane.  This  volume  is  then 
figured  to  percentage  as  directed  for  CO2. 

Notes  on  the  Process.  —  It  is  best  to  take  the  samples  as  above  directed 
rather  than  by  emptying  a  flask  filled  with  water,  for  unless  the  water  is 
very  pure  distilled  water  it  will  cause  error  by  being  alkaline  or  acid,  or 
containing  COg.  Moreover,  the  flask  should  not  be  shipped  wet  on  the 


FIG.  24. 


THE  ANALYSIS  OF  GASES  295 

inside  if  many  hours  will  elapse  before  the  analysis  is  made  for  the  wet 
surface  of  the  flask  becomes  alkaline. 

The  methane  may  be  determined  in  the  same  flask  used  for  the. deter- 
mination of  CO  2,  after  the  CO 2  titration. 

It  is  necessary  for  the  platinum  spiral  to  be  heated  yellow  hot  or  some 
methane  will  be  unburned. 

The  water  used  when  the  flask  is  immersed  to  exchange  stoppers  must 
be  absolutely  neutral  and  free  from  C02  or  error  will  be  caused. 

REFERENCES  ON  GAS  ANALYSIS: 

Bulletin  42  of  U.  S.  Bureau  of  Mines.     Mine  Gases  and  Natural  Gas. 
Bulletin  19  of  U.  S.  Bureau  of  Mines.     Natural  gas. 
Bulletin  1  of  U.  S.  Bureau  of  Mines.     Coal  gas. 
Bulletin  12  of  U.  S.  Bureau  of  Mines.     Furnace  gas. 
TREAD  WELL-HALL,  "Analytical  Chemistry,"  Vol.  II. 
WINKLER-LUNGE,  "Technical  Gas  Analysis." 
HEMPEL-DENNIS,  "Gas  Analysis." 
WHITE,  "Gas  and  Fuel  Analysis." 

THE  BLOOD  TEST  FOR  CO 

With  a  little  experience  one  can  detect  as  little  as  0.03  per 
cent.  CO  with  the  following  test:  Draw  two  drops  of  blood  from 
a  finger  and  dilute  to  200  c.c.,  when  the  solution  should  have  a 
buff-yellow  tint.  Pour  the  solution  in  two  100  c.c.  tubes.  Take 
one  of  the  tubes  into  the  room,  the  air  of  which  is  to  be  tested, 
and  allow  50  c.c.  of  the  solution  to  run  out.  /  Stopper  the  tube 
and  shake  the  solution  gently  for  10  minutes,  keeping  it  pro- 
tected from  the  light.  Then  compare  the  color  of  the  solution 
with  the  color  of  the  blood  solution  in  the  other  tube.  If  there 
was  more  than  a  trace  of  CO  in  the  air,  the  solution  with  which 
the  air  was  shaken  will  have  a  pink  tinge  as  compared  with  the 
color  of  the  other  tube. 

IODINE  PENTOXIDE  METHOD  FOR  CO 

The  most  accurate  quantitative  method  for  determining  CO  in 
very  small  amounts  is  based  on  the  reaction  I205+5CO  = 
5CO2+2I,  the  CO2  produced  being  absorbed  in  Ba(OH)2  and 
titrated  as  above  directed.  (See  Bulletin  42,  U.  S.  Bureau  of 
Mines.) 


CHAPTER  XXXII 
THE  ANALYSIS  OF  CLAYS  AND  OTHER  SILICATES 

The  methods  here  given  are  substantially  those  given  in  the  United 
States  Geological  Survey  Bulletin  422.  For  refined  methods  see  that 
bulletin.  The  methods  have  been  adapted  to  technical  use. 

Put  into  a  30  c.c.  weighed  platinum  crucible  1  gram  of  the 
finely  ground  mineral  and  ignite,  carefully  at  first,  and  finally 
to  a  bright  red  heat  for  several  minutes.  Cool  and  weigh.  Call 
the  loss  "loss  on  ignition."  It  is  chiefly  water  in  the  case  of 
clays.  Then  add  6  grams  of  pure  sodium  carbonate,  mix  the 
carbonate  with  the  mineral,  cover  the  crucible  with  a  platinum 
lid  and  fuse  at  first  cautiously,  then  at  a  high  temperature  over 
a  blast  lamp,  or  a  Meker  burner,  until  the  fusion  is  quiet  and  the 
mineral  decomposed.  The  blast  should  be  inclined,  not  directed 
vertically  against  the  crucible. 

Remove  the  cover,  seize  the  crucible  in  the  tongs,  and  allow 
the  melt  to  solidify  while  the  crucible  is  kept  tipped  on  its  side  so 
that  the  contents  will  solidify  in  a  thin  sheet  on  the  side  of  the 
crucible  and  can  be  easily  removed.  To  remove  the  cake  gently 
press  the  sides  of  the  crucible,  when  the  cake  will  crumble  to 
pieces.  Transfer  the  contents  of  the  crucible  to  a  casserole,  or 
better,  to  a  silica  dish,  dissolve  what  remains  in  the  crucible,  and 
what  spattered  on  the  lid,  with  hot  water  and  transfer  the  solution 
to  the  casserole.  Add  100  c.c.  of  hot  water  to  the  casserole,  heat 
until  the  cake  is  all  decomposed  and  no  hard  lumps  remain. 
Then  add  15  c.c.  of  HC1  gradually  with  a  cover-glass  on  the  cas- 
serole in  order  to  prevent  loss  by  frothing,  wash  out  the  crucible 
with  a  little  HC1  and  add  the  solution  to  the  casserole.  Set  the 
casserole  on  a  hot  plate  or  steam-bath  and  evaporate  to  hard 
dryness.  An  air  blast  over  the  surface  will  greatly  hasten  the 
evaporation.  .  . 

Pour  over  the  dry  mass  30  c.c.  of  1 : 1  HC1  and  heat  almost  to 
boiling  for  several  minutes,  then  add  50  c.c.  of  hot  water,  boil 

296 


ANALYSIS  OF  CLAYS  AND  OTHER  SILICATES          297 

several  minutes  and  filter  the  solution  through  an  ashless  filter. 
Transfer  as  much  of  the  silica  to  the  filter  as  is  convenient  but  do 
not  try  to  remove  the  last  trace.  Wash  the  silica  until  no  test 
for  chlorine  is  obtained  (while  the  filtrate  is  evaporating).  Add 
the  washings  and  evaporate  the  entire  filtrate  to  dryness,  dissolve 
as  before  and  filter  through  another  paper,  and  transfer  all  silica 
obtained  the  second  time  (about  1  per  cent,  of  the  silica  in  the 
sample)  to  the  paper.  This  necessitates  vigorous  use  of  a  police- 
man. Wash  the  paper  free  from  chlorine,  place  the  two  papers 
and  their  contents  in  a  platinum  crucible,  very  carefully  drive  off 
the  water  and  burn  off  the  paper.  When  the  paper  is  burned  off, 
cover  the  crucible  with  a  lid  and  ignite  the  silica  at  a  high  temper- 
ature with  a  blast  lamp  or  Meker  burner  for  at  least  15  minutes, 
for  this  long  blasting  is  necessary  to  drive  off  the  last  trace  of 
water.  Cool  and  weigh  the  crucible  and  contents.  Then 
moisten  the  silica  with  water,  add  a  few  drops  of  sulfuric  acid 
and  10  c.c.  of  HF.  Evaporate  off  the  HF  on  a  hot  plate,  in  a 
good  hood,  then  raise  the  temperature  and  drive  off  the  sulfuric 
acid  and  finally  ignite  the  crucible  to  a  bright  red  heat,  cool 
and  weigh.  The  loss  in  weight  is  the  silica. 

Add  a  few  cubic  centimeters  of  HC1  to  the  crucible  and  loosen 
the  residue,  consisting  chiefly  of  titania,  alumina,  and  oxides  of 
iron  and  phosphorus,  by  rubbing  the  bottom  with  a  policeman. 
The  residue  loosens  easily.  Pour  the  solution  into  the  filtrate 
from  the  silica. 

To  the  filtrate  from  the  silica  having  a  volume  of  about  250  c.c., 
add  a  11-cm.  filter  paper  thoroughly  macerated  by  shaking  it 
violently  in  a  flask  with  25  c.c.  of  water,  then  add  NH4OH  until 
nearly  neutralized,  heat  to  boiling  and  add  NH4OH  until  just 
barely  alkaline,  boil  for  a  minute  or  so  and  filter  (preferably  using 
suction.)  Wash  the  precipitate  two  or  three  times  with  water, 
then  wash  it  back  into  the  beaker  in  which  the  precipitation 
was  made,  dissolve  it  in  15  c.c.  HC1,  dilute  the  solution  to  100  c.c., 
heat  to  boiling  and  precipitate  with  NH4OH  as  before.  It  is 
important  that  the  solution  be  made  only  barely  alkaline  other- 
wise manganese  will  precipitate  partially.  Filter  through  the 
same  paper  as  before,  wash  with  5  per  cent.,  NH4NO3  solution 
until  free  from  chlorine,  dry  the  precipitate  of  Fe(OH)2,  A1(OH)3, 
Ti(OH)4;  PgOs,  a  little  SiO2,  etc.,  in  a  weighed  platinum  crucible, 


298  METALLURGICAL  ANALYSIS 

burn  off  the  paper  at  a  low  temperature,  then  ignite  the  precipi- 
tate over  the  blast  lamp  or  Meker  burner  for  15  minutes  with  an 
oblique  flame,  if  a  blast  is  used.  Cool  in  a  desiccator  and  weigh 
quickly  with  a  lid  on  the  crucible,  for  the  precipitate  takes  up 
moisture  from  the  air  easily  after  having  been  ignited  in  the 
presence  of  macerated  paper. 

Transfer  the  precipitate  to  a  small  beaker,  add  10  c.c.  of  HC1 
and  10  c.c.  of  1  :1  H2S04  and  evaporate  until  the  H2S04  fumes 
strongly  to  render  insoluble  the  few  milligrams  of  Si02  always 
present,  cool,  add  20  c.c.  of  water  and  heat  until  everything  but 
the  SiO2  is  in  solution.  Filter  off  the  Si02,  wash  it,  ignite  and 
weigh.  Treat  with  a  few  drops  of  H2S04  and  1  c.c.  of  HF, 
evaporate,  ignite  and  weigh.  Add  this  Si02  to  that  previously 
obtained.  It  may  possibly  contain  some  BaSO4.  This  method 
for  dissolving  the  ignited  oxides  is  excellent  when  they  have  been 
precipitated  with  macerated  filter  paper. 

In  the  filtrate  determine  the  iron  and  titania.  Determine  the 
iron  preferably  as  follows:  dilute  the  solution  to  200  c.c.  in  a 
small  flask  with  a  two-hole  stopper,  heat  to  boiling,  pass  through 
a  stream  of  H2S  till  the  iron  is  reduced,  cool,  filter  off  the  sulfur 
and  platinum  sulfide,  again  pass  a  stream  of  H2S  and  then  con- 
tinue the  boiling  while  a  stream  of  CO2  is  passed  through  until 
the  issuing  gas  does  not  blacken  a  piece  of  filter  paper  moistened 
with  lead  acetate.  Cool  while  the  CO2  continues  to  pass  and 
then  titrate  with  a  permanganate  solution.  If  titanium  is  low 
the  iron  may  be  determined  by  the  zinc-permanganate  method. 
After  the  iron  is  titrated  determine  the  titanium  by  adding  H2O2 
and  determining  the  titanium  colorimetrically  as  directed  on  page 
167.  If  it  is  suspected  that  the  precipitate  of  A1(OH)3,  etc.,  con- 
tained some  manganese,  divide  the  solution  of  the  sulfates  in  two 
equal  parts,  and  in  one  determine  the  iron  and  titanium  and 
in  the  other  determine  the  manganese  by  the  bismuthate  method. 

Subtract  the  weight  of  the  Fe203,  Ti02,  SiO2  and  P2O5  from  the 
weight  of  the  ignited  precipitate  to  get  the  weight  of  the  A1203. 
The  P2O5  must  be  determined  in  a  separate  sample  as  directed  for 
iron  ores. 

The  filtrate  from  the  A1(OH)3,  etc.,  contains  practically  all  the 
manganese,  calcium,  magnesium,  strontium,  barium,  and  pos- 
sibly traces  of  other  elements. 

If  there  is  any  manganese,  zinc,  cobalt,  nickel,  copper,  etc., 


ANALYSIS  OF  CLAYS  AND  OTHER  SILICATES 

present,  add  to  the  hot  solution  3  c.c.  of  NH4OH  and  about  the 
same  amount  of  ammonium  sulfide,  shake  well  and  filter  off  the 
sulfides.  Determine  the  manganese,  if  it  is  desired,  in  the  sulfides 
by  the  bismuthate  method  exactly  as  if  the  precipitate  were  a 
steel.  Or  the  manganese  may  be  precipitated  later  on  with  the 
magnesium  and  determined  then. 

Evaporate  the  solution  if  necessary  to  300  c.c.,  heat  to  boiling 
and  precipitate  the  calcium  and  strontium  by  adding  a  sufficient 
amount  of  ammonium  oxalate  (10  c.c.  or  more  of  saturated  solu- 
tion). The  precipitate,  if  small,  should  be  allowed  to  settle 
several  hours.  Filter  it  off  on  a  close  paper,  dry  and  ignite  the 
oxalate  to  calcium  oxide  by  ignition  in  a  platinum  crucible  over 
a  blast  for  several  minutes.  Cool  in  a  desiccator  and  weigh. 
If  the  precipitate  is  large,  it  must  be  dissolved  and  reprecipitated. 

In  the  filtrate  from  the  calcium,  precipitate  the  magnesium 
with  sodium  phosphate,  allow  to  settle  over  night  if  possible, 
filter  on  a  weighed  Gooch  crucible,  ignite  and  weigh  as  Mg2P207. 
If  manganese  is  present,  determine  it  in  the  precipitate  by  the 
bismuthate  method. 

Feldspars  often  contain  barium.  This  may  be  detected  by 
making  the  filtrate  from  the  magnesia  acid  with  sulfuric  acid  and 
precipitating  the  barium  as  barium  sulfate. 

DETERMINATION  OF  THE  ALKALIES  BY  J.  LAWRENCE  SMITH 

METHOD 

When  silicates  containing  K20  and  Na20  are  heated  with  a  mixture 
of  CaCOs  and  NH4C1,  CaCU  is  first  formed  by  double  decomposition, 
and  this  then  acts  on  the  silicates  forming  alkaline  chlorides  and  lime 
silicates.  A  red  heat  is  necessary. 

There  is  needed,  first,  pure  CaC03  free  from  K20  and  Na20.  This 
can  be  prepared  by  dissolving  marble  in  HC1,  to  saturation,  adding  a 
little  slaked  lime  to  make  the  liquid  alkaline  and  precipitate  Fe203, 
A1203  and  P205,  then  diluting  and  heating  the  liquid  and  precipitating 
the  CaC03  by  (NH4)2C03.  This  is  washed  till  free  from  HC1  and  dried. 
The  other  substance  needed  is  pure  NH4C1.  This  must  be  powdered 
and  must  volatilize  without  residue  at  a  low  re^d  heat. 

Process  of  Analysis. — Mix  1  gram  of  clay  with  1  gram  of  NH4C1. 
Grind  them  together  in  a  small  porcelain  mortar.  Add  8 
grams  of  CaCO3  and  mix  thoroughly  with  the  clay  and  NH4C1. 


300  METALLURGICAL  ANALYSIS 

Put  a  little  pure  CaC03  on  the  bottom  of  a  large  (30  to  50  c.c.) 
platinum  crucible  and  then  add  the  mixture.  Clean  out  the 
mortar  by  grinding  a  little  more  CaCO3  in  it  and  add  this  on  top 
of  the  mixture  as  a  cover.  Place  the  crucible  three-fourths 
through  a  hole  in  an  asbestos  board  in  which  the  crucible  tightly 
fits,  cover  the  crucible  with  its  lid  and  set  on  the  lid  a  large  porce- 
lain crucible  filled  with  water.  This  keeps  the  top  cool  and  pre- 
vents loss  of  vapor  of  the  alkalies. 

Now  heat  carefully,  gently  at  first,  with  a  Bunsen  flame  about 
an  inch  long  just  touching  the  crucible,  as  long  as  an  odor  of 
ammonia  is  given  off.  Then  heat  to  full  redness  for  three- 
fourths  of  an  hour  with  a  Meker  burner.  Cool  and  transfer  the 
sintered  mass  to  a  casserole.  Wash  the  crucible  and  cover  with 
hot  water  and  add  the  washings.  Digest  the  whole  until  the  mass 
slakes  to  a  fine  powder.  Now  filter  and  wash  with  hot  water 
until  the  filtrate  amounts  to  250  c.c. 

This  amount  of  washing  will  take  out  all  the  alkali,  though  the 
filtrate  will  still  react  for  chlorine,  due  to  the  fact  that  the  CaO 
retains  slowly  soluble  oxychlorides  which  it  is  impossible  to 
wash  out  completely,  and  which  will  cause  the  filtrate  to  react 
for  chlorine  indefinitely. 

To  the  hot  filtrate  add  NH4OH  and  (NH4)2C03  in  excess. 
The  calcium  separates  as  carbonate,  which  on  heating  becomes 
granular  and  easily  filtered.  Filter  and  wash  with  water  con- 
taining a  very  little  NH4OH. 

Concentrate  the  filtrate  to  small  volume  in  a  large  silica  or 
platinum  dish,  then  transfer  it  to  a  small  dish  and  finally  evapo- 
rate it  to  dryness.  Now  ignite  it  carefully  at  a  heat  not  exceeding 
a  barely  visible  red,  until  all  NH4C1  is  expelled  and  no  more 
fumes  form.  Cool,  add  a  little  water  and  a  drop  of  BaCl2,  then  a 
cubic  centimeter  of  10  per  cent.  (NH^COs  and  a  cubic  centimeter 
of  (NH4)2C204,  heat  and  filter  from  any  residue.  Add  two  or 
three  drops  of  HC1  to  the  filtrate  and  again  evaporate  to  dryness 
in  a  weighed  dish.  Dry,  ignite  carefully  as  before  and  weigh  as 
KCl+NaCl.  The  chlorides  must  be  white  and  dissolve  without 
residue  in  water.  If  there  be  a  residue,  weigh  it. 

To  the  water  solution,  about  10  c.c.  in  volume,  add  an  ex- 
cess of  platinic  chloride,  and  evaporate  carefully  until  only  a 
drop  of  liquid  is  left.  Add  20  c.c.  of  alcohol  (80  per  cent.)  and 


ANALYSIS  OF  CLAYS  AND  OTHER  SILICATES          301 

let  stand  till  the  platinum  salts  dissolve.  Filter  onto  a  weighed 
Gooch  filter.  Wash  the  K2PtCl6  with  80  per  cent,  alcohol.  Dry 
and  weigh.  Calculate  the  KgO  from  the  weight  of  this  and  the 
Na2O  from  the  remainder,  after  deducting  the  KC1,  calculated 
from  the  K^O,  from  the  mixed  chlorides. 

The  strength  of  the  alcohol  is  important.  The  K^PtCle  is 
practically  insoluble  in  80  per  cent,  alcohol,  but  the  Na2PtCl6 
will  dissolve  in  it.  Time  must  be  given  to  secure  complete  solu- 
tion of  this  latter  salt. 

Notes  on  Silicate  Analysis. — The  above  methods  are  quite  accurate 
and  for  technical  purposes  may  sometimes  be  shortened.  There  are, 
however,  some  small  errors  to  be  corrected  for  in  exact  work. 

The  loss  on  ignition  includes  hygroscopic  water,  combined  water, 
carbon  dioxide  from  carbonates,  organic  matter,  sulfur,  oxygen  from 
MnO2,  while  the  sample  may  take  up  oxygen  by  oxidation  of  ferrous 
iron,  etc.  For  a  full  discussion  see  U.  S.  G.  S.  Bulletin  422. 

When  evaporations  are  made  in  porcelain  casseroles  and  precipitations 
in  glass  beakers  a  milligram  or  two  of  SiC>2  and  A1203,  etc.,  will  be  ob- 
tained from  them.  To  get  exact  results  a  blank  must  be  run. 

If  the  sample  contains  fluorine  some  silica  will  be  lost  as  tetrafluoride. 

The  precipitate  of  iron,  aluminium,  and  titanium  hydroxides  will 
generally  be  contaminated  with  a  small  amount  of  manganese,  always 
with  one  or  more  milligrams  of  silica,  all  the  phosphorus  in  the  sample, 
vanadium  if  it  be  present,  chromium,  zirconium,  etc.  For  exact  work 
these  must  be  determined  in  the  precipitate.  Sometimes  a  sample  of 
clay  or  slag  may  have  several  per  cent,  of  P205  which  should  be  deter- 
mined as  in  an  iron  ore. 

The  use  of  macerated  filter  paper  makes  the  filtration  of  a  large  pre- 
cipitate of  A1(OH)3  much  easier  and  also  greatly  aids  the  subsequent 
solution  of  the  ignited  precipitate.  In  fact  it  is  generally  soluble  in  1:2 
sulfuric  acid. 

When  iron  is  reduced  there  should  be  not  more  than  2  or  3  per  cent, 
of  sulfuric  acid  present. 

The  precipitate  of  A1(OH)3,  etc.,  must  be  washed  with  an  ammonium 
salt,  not  pure  water.  Clays  always  contain  at  least  traces  of  titania. 

The  precipitate  of  calcium  oxalate  is  generally  contaminated  with  a 
small  amount  of  aluminium  hydroxide,  iron  hydroxide,  magnesia,  sodium 
and  strontium.  To  remove  these  (except  strontium)  the  precipitate  is 
ignited,  dissolved  in  HC1,  made  alkaline  with  ammonia,  boiled,  alum- 
inium filtered  off  and  the  calcium  precipitated  again. 

The  precipitate  of  magnesium  phosphate  is  likewise  apt  to  be  con- 


302  METALLURGICAL  ANALYSIS 

laminated  with  barium,  calcium,  manganese,  alumina,  etc.,  and  unless 
two  precipitations  are  made  the  precipitate  is  apt  to  contain  too  much 
ammonium  phosphate  and  be  too  heavy.  Manganese  may  be  deter- 
mined colorimetrically  in  the  precipitate. 

In  the  alkali  determination  especial  care  must  be  taken  to  make  sure 
that  the  heat  is  not  so  high  at  first  as  to  drive  off  the  ammonium  chloride 
instead  of  breaking  it  up  to  form  CaCl2  and  ammonia. 

ANALYSIS  OF  BLAST-FURNACE  SLAGS 

The  slags  made  in  the  iron  blast  furnace  are  essentially  silicates 
of  lime,  magnesia  and  alumina.  They  usually  contain,  however, 
small  percentages  of  iron,  manganese,  and  sulfur.  Phosphorus  is 
rarely  present  in  more  than  traces.  Titanium  and  other  rarer  ele- 
ments, if  present  in  the  ore,  will  be  found  in  the  slag.  Slags  that  are 
high  in  alumina  and  magnesia,  will  sometimes  contain  small  crystals  of 
spinel  (MgOAl203).  As  this  substance  is  neither  attacked  by  HC1, 
decomposed  by  fusion  with  Na2C03,  nor  dissolved  by  HF,  it  will  be 
found  in  the  silica  obtained  in  the  analysis.  Spinel  can  be  decomposed 
by  prolonged  treatment  with  hot  H2S04  diluted  with  its  own  volume  of 
water. 

Most  furnace  slags  can  be  decomposed  by  treatment  with  HC1, 
especially  if  they  have  been  suddenly  cooled  from  the  molten  state. 
Slags  that  are  not  decomposed  by  HC1  must  be  fused  with  Na2C03. 

Slags  frequently  contain  metallic  iron  in  small  grains;  this  should  be 
taken  out  of  the  crushed  sample  by  a  magnet.  If  the  slag  itself  is 
magnetic  the  metal  grains  can  be  picked  out  under  a  magnifying  glass 
with  pincers.  The  sample  must  finally  be  ground  in  an  agate  mortar 
to  an  impalpable  powder. 

The  exact  analysis  of  slags  is  carried  out  the  same  as  the  analysis  of 
silicates,  as  given  above.  If  the  slag  has  much  manganese  the  first  pre- 
cipitation of  alumina  and  ferric  hydroxide  must  be  made  by  the  basic 
acetate  method,  otherwise  they  will  retain  considerable  manganese. 

If  the  slag  is  soluble  in  HC1,  the  fusion  with  sodium  carbonate  is 
unnecessary. 

Short  Method. — For  the  purpose  of  furnace  control,  it  is  usu- 
ally sufficient  to  know  the  percentages  of  silica,  alumina,  lime  and 
magnesia  in  a  slag.  These  can  be  determined  with  sufficient 
accuracy  by  the  following  process. 

The  Determination  of  the  CaO  and  the  MgO. — Weigh  1  gram 
of  the  sample  into  a  casserole,  add  30  c.c.  of  water  and  stir  the 
slag  up  into  it  to  prevent  caking  and  the  separation  of  gelatinous 


ANALYSIS  OF  CLAYS  AND  OTHER  SILICATES          303 

silica  on  the  addition  of  acid.  Now  add  20  c.c.  of  HC1  and  heat. 
Everything  should  dissolve  except  a  few  flakes  of  Si02  and  possi- 
bly a  little  carbon  or  sulphur.  There  should  be  no  gritty  residue. 
Cover  the  casserole,  and  boil  the  solution  to  dryness  to  separate 
most  of  the  silica. 

Now  add  10  c.c.  of  HC1,  a  few  drops  of  HN03,  and  then  50 
c.c.  of  water.  Boil  to  dissolve  the  bases  and  then  transfer  the 
contents  of  the  casserole,  without  filtering,  to  a  500  c.c.  graduated 
flask.  Dilute  the  liquid  to  about  300  c.c.  and  add  NH4OH  until 
the  alumina  separates,  but  avoid  a  large  excess.  If  the  sample 
contains  more  than  a  few  tenths  per  cent,  of  manganese,  add  2  or 
3  c.c.  of  ammonium  sulfide  to  precipitate  it  with  the  alumina. 
Heat  the  contents  of  the  flask  to  boiling  and  boil  for  three  min- 
utes. Cool  the  liquid  and  dilute  it  to  the  mark  with  water  free 
from  CO2.  Mix  the  contents  of  the  flask  thoroughly  and  then 
filter  off  250  c.c.  through  a  dry  filter. 

Determine  'the  lime  and  magnesia  in  this  volumetrically  as  in 
a  limestone.  If  ammonium  sulfide  was  used,  add  HC1  to  the 
filtered  solution,  till  it  is  neutral  and  then  about  5  c.c.  in  excess. 
Boil  till  the  H2S  is  expelled,  then  add  0.5  gram  of  KC1O3  and  heat 
till  the  separated  sulfur  is  dissolved.  Now  add  NH4OH  in  excess 
and  proceed  with  the  determination  of  the  lime  as  before.  Should 
a  trace  of  MnO2  separate  on  adding  the  ammonium  hydroxide, 
continue  the  heating  till  it  dissolves  and  the  solution  is  nearly 
colorless,  before  precipitating  the  lime. 

The  Determination  of  the  SiO2  and  the  A12O3.— Weigh  0.5 
gram  of  the  sample  into  a  casserole,  treat  it  with  water  and  HC1 
and  evaporate  to  dryness  as  before,  in  this  case,  however,  the  dry 
residue  must  be  heated  till  all  HC1  is  expelled,  avoiding  a  tem- 
perature of  over  120°. 

Take  up  the  residue  in  water  and  HC1,  filter  and  weigh  the 
silica.  It  is  well  to  evaporate  the  solution  to  dryness  a  second 
time  before  filtering  off  the  silica,  as  this  makes  the  filtration 
more  rapid. 

The  residue  is  usually  taken  to  be  silica  but  is  liable  to  contain 
traces  of  Fe2O3,  Ti02,  and  spinel.  It  may  be  tested  with  HF 
and  any  fixed  residue  deducted.  (See  page  298.)  If  this  is 
done,  the  silica  should  be  separated  by  a  double  evaporation 
as  it  is  not  all  precipitated  by  a  single  one.  Ordinarily  the 


304  METALLURGICAL  ANALYSIS 

impurities  present  will  about  balance  the  silica  lost  and  so  the 
gross  weight  is  nearly  correct. 

The  alumina  is  now  determined  in  the  filtrate  from  the  silica. 

In  the  absence  of  much  manganese  this  can  be  done  by  pre- 
cipitation with  NH^H  as  in  the  analysis  of  a  limestone,  taking 
care  to  have  plenty  of  NH4C1  present  and  to  redissolve  the 
first  precipitate  which  is  likely  to  contain  a  little  lime.  The 
precipitate  should  be  washed  by  decantation  until  free  from 
chlorides  and  then  transferred  to  the  filter.  The  precipitate 
contains  all  iron,  phosphoric  acid  and  titanic  acid  in  the  slag. 

If  the  slag  contains  much  manganese,  the  alumina  must  be 
separated  from  it  by  a  basic  acetate  precipitation  as  described 
on  page  73.  The  precipitate  is  then  redissolved  in  HC1  and  the 
alumina,  now  free  from  manganese,  precipitated  with  NH4OH. 

Determination  of  A12O3  as  Phosphate. — Dilute  the  filtrate 
from  the  silica  in  a  300  c.c.  beaker  to  about  200  c.c.  To  the 
cold  solution  add  about  15  c.c.  of  a  saturated  solution  of  sodium 
phosphate,  and  then  NH4OH  cautiously  and  with  constant  stir- 
ring until  a  slight  permanent  precipitate  forms.  Now  add  5 
drops  of  HC1  which  should  dissolve  the  precipitate  and  leave 
a  clear  solution.  Then  add  with  constant  stirring  20  c.c.  of  a 
saturated  solution  of  sodium  thiosulfate.  If  much  iron  is  pres- 
ent as  in  the  case  of  an  ore,  the  solution  will  turn  nearly  black, 
but  on  continuing  the  stirring  will  grow  lighter  as  the  iron 
is  reduced  and  finally  a  white  precipitate  of  AlPO4-|-Ti3(PO4)4 
will  be  thrown  down  mixed  with  a  large  quantity  of  S.  Cover 
the  beaker  and  heat  the  solution  till  it  boils.  When  boiling  add 
20  c.c.  of  a  solution  consisting  of  100  grams  of  sodium  acetate, 
200  c.c.  of  acetic  acid,  sp.  gr.  1.04,  and  water  to  make  500 
c.c.  Boil  the  solution  10  minutes  longer  or  till  the  precipitate 
coagulates. 

Let  the  precipitate  settle,  filter,  and  wash  the  precipitate  ten 
times  with  hot  water.  Put  the  wet  filter  into  a  crucible,  ignite 
at  a  low  heat  to  burn  off  the  paper  and  sulfur,  and  then  ignite 
over  the  blast  lamp. 

The  residue  is  AlPO4+Ti3(PO4)4  and  contains  0.418  A12O3  if 
Ti  is  absent. 

REFERENCE : 

•   J.  M.  CAMP,  Iron  Age,  LXV,  17. 


ANALYSIS  OF  CLAYS  AND  OTHER  SILICATES'         305 

When  this  method  is  applied  to  ores  the  first  precipitate  is  likely  to 
contain  a  little  iron.  This  can  be  removed  by  dissolving  and  reprecipi- 
tating  it  in  the  same  way. 

Sulfur  and  iron  can  be  determined  in  slags  as  in  iron  ores. 

Sulfur. — The  sulfur  in  slags  is  present  almost  wholly  as  cal- 
cium sulfide.  It  can  be  determined  approximately  by  adding  150 
c.c.  of  water  to  0.5  gram  of  the  very  finely  pulverized  slag  and 
titrating  with  the  standard  iodine  solution  used  for  sulfur  in  iron. 

Stir  the  mixture  of  slag  and  water  and  add  3  or  4  c.c.  of  starch 
solution,  then  run  in  the  iodine  till  the  blue  color  develops.  Now 
add  15  c.c.  of  concentrated  HC1,  stir  and  add  the  iodine  again 
until  the  color  no  longer  disappears. 

If  1  c.c.  of  the  iodine  equals  0.0005  gram  S,  each  cubic  centi- 
meter taken  will  be  equivalent  to  0. 1  per  cent,  sulfur  in  the  slag. 

REFERENCE : 

J.  Anal  and  App.  Chem.,  Vol.  VII,  No.  5. 

It  is  probably  more  accurate  to  evolve  the  H2S  in  a  flask  as 
for  pig-iron.  Put  5  grams  of  granular  zinc  into  the  flask,  then  add 
0.25  to  0.5  gram  of  the  very  finely  ground  slag.  The  hydrogen 
from  the  Zn  carries  over  the  H2S  from  the  slag.  This  is  absorbed 
by  an  ammoniacal  cadmium  solution  and  titrated  as  usual. 
See  Camp,  "  Methods  of  Analysis  in  the  Laboratories  around 
Pittsburgh  2nd  ed.,  p.  147. 

Manganese  in  slag  can  be  determined  as  in  iron  ores.  Small  percent- 
ages are  best  estimated  by  the  bismuthate  method. 

MINERAL  ANALYSIS  OF  CLAYS 

This  is  sometimes  very  useful.  It  depends  upon  the  fact  that  kaolin 
is  soluble  in  sulfuric  acid  with  the  liberation  of  silica  soluble  in  NaOH, 
while  quartz  and  feldspars  are  not  appreciably  soluble  in  either  of  the 
above  reagents  unless  extremely  finely  ground. 

Process  of  Analysis. — Place  2  grams  of  the  clay  in  a  250  c.c. 
flask  and  add  100  c.c.  of  water  and  20  c.c.  of  strong  sulfuric  acid. 
Boil  down  the  solution  until  the  acid  fumes  strongly.  Cool,  add 
50  c.c.  of  water,  heat  until  the  A12(SO4)3  is  all  in  solution  and 
filter  through  a  double  filter.  Wash  well  with  water,  wash  the 
residue  back  into  the  flask  and  add  50  c.c.  of  a  7  per  cent,  sodium 
20 


306  METALLURGICAL  ANALYSIS 

hydroxide  solution,  heat  to  boiling  for  five  minutes,  and  filter 
through  the  same  paper  without  transferring  the  residue  thereto. 
Again  add  50  c.c.  of  7  per  cent,  soda,  heat  to  boiling  and  shake  the 
solution,  transfer  the  residue  to  the  paper,  filter,  wash  well  with 
water,  then  with  dilute  HC1,  ignite  and  weigh.  The  decrease  in 
weight  is  "clay  substance."  Fuse  the  residue  with  sodium  car- 
bonate, and  determine  the  silica  in  it.  This  subtracted  from 
the  weight  of  the  clay-free  residue  gives  the  alumina  and  alkalies 
in  the  feldspars,  which  multiplied  by  3  gives  the  amount  of  feld- 
spar present;  for  the  alumina  and  alkalies  in  the  common  feld- 
spars will  average  about  one-third  of  them.  The  sum  of  the  clay 
substance  and  feldspars  subtracted  from  100  will  give  the  quartz 
in  the  sample. 

The  results  are  only  approximate  and  the  method  does  not 
apply  to  red  clays  of  clays  containing  limestone. 

DETERMINATION    OF   SILICA,    ALUMINA,   LIME   AND    MAGNESIA 

IN  IRON  ORES 

Silica. — Put  2  grams  of  the  ore  in  a  12-cm.  porcelain  dish  with 
cover;  add  30  c.c.  of  strong  hydrochloric  acid,  and  heat  for  half 
an  hour  or  until  the  action  of  the  acid  has  ceased,  but  do  not 
allow  the  acid  to  boil.  Cool  the  solution  for  a  few  minutes ;  dilute 
to  twice  the  volume  with  hot  water,  and  filter  into  another  dish. 
Wash  the  residue  with  hot  water  until  the  water  runs  through 
colorless;  ignite  the  filter  and  residue  in  a  platinum  crucible,  and 
fuse  the  impure  silica  with  about  five  times  its  own  weight  of 
Na2CO3.  When  the  fusion  has  become  tranquil  place  in  it  a 
stout  piece  of  platinum  wire  about  8  cm.  long,  with  the  end  that 
is  put  into  the  crucible  flattened  and  bent  at  right  angle;  incline 
the  crucible  slightly,  then  remove  the  heat,  and  hold  the  wire  in 
position,  touching  the  bottom  of  the  crucible,  until  the  mass 
solidifies.  Now  heat  the  crucible  rapidly  and  uniformly  with 
the  blast-lamp  or  Bunsen  burner;  lift  out  the  melt  with  the  wire 
as  soon  as  it  is  loose,  and  place  it  in  the  dish  in  which  the  ore  was 
first  treated.  Cover  the  dish,  add  about  30  c.c.  of  hot  water  to 
disintegrate  the  fusion,  then  add  hot  water  to  the  crucible  and 
dislodge  adhering  substance  as  completely  as  possible  with  a  glass 
rod.  Add  the  washings  from  the  crucible  to  the  main  portion  in 


ANALYSIS  OF  CLAYS  AND  OTHER  SILICATES  '       307 

the  dish,  and  acidify  the  whole  with  15  c.c.  of  strong  hydrochloric 
acid.  Cleanse  the  crucible  thoroughly  by  warming  a  little 
hydrochloric  acid  in  it,  and  when  the  solid  matter  is  completely 
disintegrated,  scrub  the  crucible  with  a  policeman,  and  rinse  again. 
Evaporate  the  solutions  in  both  dishes  to  dryness,  and  continue 
to  heat  for  an  hour  at  about  120°C.  Add  to  the  dish  containing 
most  of  the  iron  15  c.c.  of  strong  hydrochloric  acid,  and  warm 
until  the  ferric  oxide  is  dissolved.  To  the  other  dish,  containing 
most  of  the  silica,  add  just  enough  dilute  hydrochloric  acid  to 
moisten  the  residue  and  warm,  then  add  about  30  c.c.  of  hot 
water  and  boil.  Pour  the  solution  from  this  dish  into  the  other 
dish,  keeping  back  most  of  the  silica,  filter  the  contents  of  both 
dishes  into  a  200  c.c.  graduated  flask,  wash  both  dishes  carefully, 
using  a  rubber-tipped  rod  to  remove  adhering  matter,  and  wash 
the  filter  free  from  chlorides.  Set  aside  the  filtrate  for  the 
determination  of  alumina,  etc.  Ignite  the  residue,  and  weigh  as 
impure  SiO2.  Add  two  drops  of  sulfuric  acid,  10  c.c.  of  HF, 
evaporate  to  dryness,  ignite  and  weigh.  The  loss  is  SiO2. 

For  exact  results  two  evaporations  to  dryness  are  necessary. 
Otherwise  the  SiO2  will  be  slightly  low. 

Clean  the  residue  out  of  the  crucible  with  a  few  cubic  centi- 
meters of  HC1  using  a  policeman,  and  add  the  solution  to  the 
filtrate  from  the  SiC>2. 

Alumina. — The  aluminium  and  iron  are  first  separated  from 
the  manganese  and  other  bases  by  the  basic  acetate  pre- 
cipitation; the  resulting  hydroxides  are  dissolved  with  hydro- 
chloric acid,  and  the  aluminium  is  separated  from  the  solution 
as  phosphate.  Having  cooled  the  filtrate  from  the  silica  in 
the  flask  and  made  the  solution  up  to  the  mark,  transfer  one- 
half  of  the  solution  to  a  600  c.c.  beaker.  Add  10  c.c.  of  strong 
hydrochloric  acid;  heat  to  boiling,  cool,  add  NH4OH  until  a 
very  slight,  permanent  precipitate  forms,  while  the  solutions 
remain  slightly  acid,  then  add  25  c.c.  of  20  per  cent,  ammonium 
acetate  solution;  dilute  to  about  450  c.c.  with  hot  water;  boil 
for  one  minute,  and  allow  to  stand  until  the  precipitate  settles. 
While  heating  the  liquid,  stir  it  frequently  to  prevent  "  bumping," 
and  turn  down  the  flame  as  it  begins  to  boil.  When  the  pre- 
cipitate has  settled,  decant  and  filter  the  liquid  through  a  10-cm. 
ribbed  funnel  with  the  paper  cut  to  fit.  Rinse  the  beaker  once, 


308  METALLURGICAL  ANALYSIS 

and  wash  the  precipitate  three  times  with  hot  water.  Save  the 
filtrate  for  the  determination  of  manganese,  etc.  Place  the  beaker 
in  which  the  precipitation  was  made  under  the  filter,  and  dis- 
solve the  precipitate  with  hot  hydrochloric  acid  (1:1)  and  wash 
with  hot  water,  making  up  the  volume  of  the  solution  to  about 
300  c.c.  Add  to  the  solution  30  c.c.  of  saturated  ammonium 
phosphate,  then  add  NH4OH  until  a  slight  precipitate  appears, 
and  dissolve  this  with  a  few  drops  of  hydrochloric  acid.  Now 
add  to  the  clear  solution  50  c.c.  of  10  per  cent,  sodium  thio- 
sulfate  solution;  stir  until  a  white  precipitate  forms,  place  the 
beaker  over  a  flame,  and  just  before  the  liquid  begins  to  boil 
add  12  c.c.  of  ammonium  acetate  and  8  c.c.  of  strong  acetic 
acid.  After  boiling  for  10  minutes,  filter  the  liquid  rapidly, 
keeping  the  precipitate  covered  with  the  liquid.  Wash  the 
filter  and  precipitate  with  hot  water  until  free  from  chlorides; 
ignite  in  a  porcelain  crucible,  and  weigh  as  A1PO4.  Titania  if  in 
the  ore  will  contaminate  the  A1P04.  Two  precipitations  are 
necessary  for  the  best  results. 

Manganese. — From  the  filtrate  from  the  basic  acetate  sepa- 
ration of  the  iron  and  aluminium,  precipitate  the  manganese 
as  directed  under  the  acetate  method  for  manganese.  If  the 
precipitate  is  small,  it  should  be  washed  well  and  the  manganese 
determined  in  it  by  the  bismuthate  method. 

With  ores  containing  as  much  as  2  per  cent,  of  manganese  a 
double  precipitation  of  iron  and  aluminium  hydroxides  should 
be  made. 

Lime  and  Magnesia. — Concentrate  the  filtrate  from  the 
manganese  determination  to  half  its  volume,  add  15  c.c.  of 
ammonium  oxalate  solution,  and  NH4OH  until  alkaline,  and 
heat  just  below  the  boiling-point  until  the  precipitate  settles 
readily.  If  there  is  no  immediate  precipitation,  concentrate 
the  solution  to  about  100  c.c.,  before  adding  the  NH4OH;  boil 
for  15  minutes  and  filter.  Wash  the  precipitate  free  from 
chlorides,  ignite  to  constant  weight  with  the  blast-lamp,  and 
weigh  as  CaO. 

Cool  the  above  filtrate;  precipitate  the  magnesia  by  adding 
10  c.c.  of  sodium  phosphate  solution  and  10  c.c.  of  NH4OH,  stir 
well,  and  set  aside  for  12  hours.  Filter  on  a  9-cm.  paper;  wash 
with  the  ammonia  and  ammonium  nitrate  solution;  ignite  at  the 


ANALYSIS  OF  CLAYS  AND  OTHER  SILICATES  309 

lowest  temperature  necessary  to  burn  off  the  paper,  and  weigh 
as  Mg2P2O7. 

If  an  accident  happens  to  any  of  the  above  determinations 
use  the  other  half  of  the  filtrate  from  the  silica  for  another 
analysis. 

PHENYLHYDRAZINE  METHOD  FOR  ALUMINA 

The  alumina  may  be  determined  as  follows:  Dissolve  several 
grams  of  the  ore  in  HC1  and  filter,  ignite  the  residue,  decompose 
it  with  HF,  evaporate  to  dryness  with  a  drop  of  H2SO4,  dissolve 
in  HC1  and  add  to  the  main  solution.  Dilute  to  250  c.c.,  nearly 
neutralize,  and  reduce  the  iron  with  NH4HSO3.  If  the  solution 
turns  deep  red  (ferric  sulphite),  it  is  not  acid  enough,  and  a  few 
drops  of  hydrochloric  acid  should  be  added,  for  the  sulphite  itself 
does  not  reduce  ferric  salts,  at  least  not  with  rapidity.  Now 
quickly  bring  to  neutrality  with  ammonia,  and  then  add  several 
drops  cf  dilute  hydrochloric  acid.  If  this  last  operation  is  done 
too  slowly  the  oxygen  of  the  air  helps  to  form  a  little  ferric  hy- 
droxide which  does  not  always  readily  dissolve  in  the  dilute  acid. 
Finally,  add  from  1  to  3  c.c.  of  phenylhydrazine,  according  to  the 
weight  of  the  alumina  to  be  precipitated.  If  too  little  has  been 
used,  a  few  drops  added  to  the  filtrate  will  disclose  the  mistake. 
Stir  until  the  precipitate  has  become  sufficiently  flaky  and  allow  to 
settle.  The  supernatant  liquid  will  now  be  plainly  acid  to  litmus. 
One  need  not  be  disturbed  if  the  precipitate  has  a  brownish  color, 
for  it  is  not  due  to  ferric  hydroxide,  but  to  the  coloring  matter 
contained  in  all  phenylhydrazine  which  has  not  been  freshly  dis- 
tilled. When  the  determinations  are  allowed  to  stand  too  long 
the  air  increases  this  oxidation  product,  and  a  brown  insoluble 
scum  forms  on  the  surface  of  the  liquid  and  on  the  sides  of  the 
vessel,  which  is  rather  troublesome  to  the  analyst.  Fortunately 
equilibrium  appears  to  be  established  in  a  short  time.  The  ves- 
sels need  not  stand  more  than  an  hour,  at  any  rate.  The  pre- 
cipitate is  washed  by  a  solution  of  phenylhydrazine  sulphite  made 
by  adding  cold  saturated  sulphurous  acid  to  a  little  phenylhy- 
drazine until  the  crystalline  sulphite  first  formed  dissolves  in  the 
excess.  The  solution  has  an  acid  reaction.  Five  to  10  c.c.  of 
this  are  used  in  100  c.c.  of  hot  water. 

Ignite  the  precipitate  and  weigh  the  A12O3,  TiO2,  P2O5  and 
V2O4  if  present.  Determine  the  Ti02,  P2O5  and  V2O4  and  obtain 
the  A12O3  by  difference. 


CHAPTER  XXXIII 
SOFTENING  WATER  FOR  BOILER  USE 

The  scale-forming  materials  in  water  are  CaH2(C03)2,  MgH2(C03)2, 
CaS04,  MgS04,  CaCl2,  MgCl2,  Fe2(S04)3,  Si02,  A12(S04)3,  and  other 
salts.  The  most  common  compounds  which  give  trouble  in  boilers  by 
causing  scale  are  the  first  four  given  above,  except  in  the  case  of  mine 
water  when  sulfates  of  iron  and  alumina  are  frequently  present. 

Water  is  softened  by  adding  lime  (CaO)  and  soda  ash  (Na2C03).  The 
reactions  are: 

CaH2(CO3)2+CaO  =  2CaC03+H20. 
MgH2(C03)2+2CaO  =  Mg(OH)2+2CaC03. 
MgS04+CaO+H20  =  CaS04+Mg(OH)2. 


To  determine  the  amount  of  lime  and  soda  ash  to  add  to  soften 
the  water  proceed  as  follows: 

Put  in  a  250  c.c.  Jena  flask  200  c.c.  of  the  water  to  be  tested, 
add  50  c.c.  of  saturated  lime  water  and  heat  to  boiling.  Cool, 
shake  well  and  filter  through  a  rapid  filter,  wash  three  times  with 
pure,  freshly  boiled  water,  and  titrate  the  filtrate  with  N/28 
HC1,  using  methyl  orange  as  indicator.  Treat  200  c.c.  of  freshly 
boiled  distilled  water  in  exactly  the  same  way,  being  careful  to 
use  the  same  amount  of  methyl  orange  in  both  cases  and  to  finish 
at  the  same  depth  of  color.  The  number  of  cubic  centimeters 
of  standard  HC1  used  the  second  time,  minus  the  number  of 
cubic  centimeters  used  the  first  time,  multiplied  by  5  gives  the 
parts  of  lime  to  add  to  a  million  parts  of  water. 

Now  add  to  the  titrated  water  in  a  porcelain  dish  30  c.c.  of 
N/14  Na2CO3,  heat  to  boiling,  cool,  filter  and  titrate  the  excess 
of  soda.  The  sodium  carbonate  precipitates  both  the  CaCU 
made  in  the  first  titration  and  the  CaSO4>  etc.,  in  the  water. 
Therefore,  to  calculate  the  amount  of  sodium  carbonate  neces- 
sary to  soften  the  water  subtract  from  2X30  =  60,  the  total 
amount  of  N/28  HC1  that  has  been  used  in  both  titrations  and 
multiply  by  9.45. 

310 


SOFTENING  WATER  FOR  BOILER  USE  311 

To  determine  the  amount  of  carbonate  or  "temporary"  hard- 
ness in  water,  it  is  only  necessary  to  titrate  it  with  a  standard 
acid  with  methyl-orange  indicator.  The  carbonate  hardness  is 
due  to  the  bicarbonates  of  calcium  and  magnesium,  CaH2(CO3)2 
and  MgH2(C03)2,  which  are  alkaline  to  methyl  orange  because 
they  are  salts  of  strong  bases  and  a  very  weak  acid  and  hydrolize, 
thus, 

CaH2(CO3)2+2HOH  =  Ca(OH)2+2H2CO3. 

To  make  the  tit  ration,  place  100  c.c.  of  the  water  in  each  of  two 
Nessler  tubes,  add  to  each  five  drops  of  methyl-orange  solution 
and  titrate  the  water  in  one  of  the  tubes  until  it  has  a  slight 
reddish  color  when  compared  with  the  color  in  the  other  tube. 
The  reaction  is  CaH2(C03)2+2HCl  =  CaCl2+2H2CO3  and  simi- 
larly for  the  magnesium  salt.  The  cubic  centimeters  of 
standard  HC1  multiplied  by  its  normality  and  by  50  gives  the 
results  in  milligrams  of  carbonates  present  figured  as  CaCO3. 
Thus  if  5  c.c.  of  N/10  HC1  were  used,  the  result  would  be 
5X0.10X50  =  25  mg.  of  CaC03  per  100  c.c.  or  250  parts  of 
CaCO3  per  million  of  water. 

To  determine  the  sulfate  or  " permanent"  hardness,  evaporate 
100  c.c.  to  hard  dryness  in  a  platinum,  or  silica,  or  nickel  dish  (not 
in  a  glass  vessel)  with  25  c.c.  of  N/10  Na2CO3,  dissolve  the  excess 
of  Na2CO3  in  pure  distilled  water,  filter  and  wash  the  paper  well. 
Titrate  the  filtrate  in  a  Nessler  tube  as  directed  for  the  titration 
of  temporary  hardness  with  the  standard  acid,  using  methyl- 
orange  indicator.  The  cubic  centimeters  of  N/10  soda  con- 
sumed multiplied  by  6.8  gives  the  permanent  hardness  in  terms 
of  milligrams  of  CaSO4  present.  This  multiplied  by  10  gives  the 
parts  per  million.  Instead  of  boiling  to  dryness  with  sodium 
carbonate,  it  is  quicker  and  accurate  to  simply  boil  a  few  minutes 
with  a  mixture  of  equal  parts  of  N/10  sodium  carbonate  and 
sodium  hydroxide,  filter  and  titrate. 

REFERENCES: 

DRAVVE,  Z.  angew.  Chern.,  XXIII,  52. 
PROCTOR,  J.  Soc.  Chem.  Ind.,  Jan.  15,  1904. 

Methyl-orange  Solution. — Dissolve  0.025  gram  of  the  sodium 
salt  in  100  c.c.  of  water  and  add  0.7  c.c.  of  N/10  HC1. 


312  METALLURGICAL  ANALYSIS 

In  the  examination  of  a  new  supply  of  water  for  boiler  purposes 
it  is  safest  to  make  a  complete  analysis  in  addition  to  the  above 
softening  tests. 

Outline  Process  for  the  Analysis. — First,  evaporate  100  c.c.  of 
the  clear  water  (filtered  if  necessary)  to  dryness  in  a  weighed 
platinum  dish,  and  dry  at  100°  to  constant  weight.  This  gives 
the  " total  solids."  After  weighing  the  dish  ignite  it  very  cau- 
tiously, not  passing  a  barely  visible  red  heat,  until  the  residue 
becomes  nearly  white.  Weigh  again  after  cooling  in  a  desiccator. 
The  loss  is  water  of  combination  and  organic  matter,  and  the 
residue  is  the  fixed  mineral  matter. 

Second,  test  the  water  for  chlorine.1  If  it  contains  more  than 
a  trace,  the  amount  may  be  determined  by  titrating  100  c.c.  of 
the  water  with  a  standard,  solution  of  AgNO3,  adding  a  little 
neutral  potassium  chromate  to  serve  as  an  indicator.  A  slight 
exces's  of  AgNO3  gives  the  reddish  color  of  silver  chromate. 

The  small  excess  of  the  silver  solution  required  to  give  the  red 
color  that  forms  the  end  reaction  can  be  determined  by  adding 
1  c.c.  of  a  standard  solution  of  NaCl  (1  c.c.  equals  1  mg.  Cl)  to 
100  c.c.  of  distilled  water,  and  titrating  this  in  the  same  way. 
The  excess  of  the  silver  solution  over  that  required  for  the  chlorine 
present  is  the  amount  that  must  be  deducted  from  that  used  in 
the  regular  titration. 

Third,  acidulate  1  liter  with  5  c.c.  HC1,  evaporate  to  dryness 
in  a  platinum  dish,  adding  it  to  the  dish  a  little  at  a  time.  Take 
up  the  residue  with  HC1  and  water,  and  determine  the  SiO2, 
Fe203  and  A12O3,  CaO  and  MgO  exactly  as  in  the  case  of  lime- 
stone. In  filtering  off  the  8162  care  must  be  taken  that  no  CaSO4 
(which  is  frequently  present  in  considerable  quantity)  be  left  un- 
dissolved  with  the  Si(>2.  It  can  all  be  dissolved  with  water  and 
HC1. 

For  ordinary  work  where  the  amount  of  Si(>2  is  usually  very 
trifling  and  of  no  technical  importance,  the  evaporation  to  dry- 
ness  can  be  omitted.  In  this  case  evaporate  1  liter  of  the  water 
with  5  c.c.  of  HC1  in  a  large  beaker,  to  about  100  c.c.  Add  an 
excess  of  NH4OH  and  filter  from  the  precipitate  of  Fe(OH)3, 
A1(OH)3  and  Si02.  Care  must  be  taken  to  have  enough  NH4C1 

1  See  FRESENIUS,  "Quantitative  Analysis." 

MELLOR,  "Quantitative  Inorganic  Analyses"  (1913). 


SOFTENING  WATER  FOR  BOILER  USE  313 

present  to  prevent  any  precipitation  of  the  magnesia.  The  CaO 
and  MgO  are  determined  in  the  filtrate  as  before. 

Fourth,  acidulate  500  c.c.  of  the  water  with  1  c.c.  of  HC1  and 
evaporate  to  100  c.c.  Filter  if  necessary  and  determine  the  SO3 
by  precipitation  with  BaCl2. 

The  alkalies  may  be  determined  closely  enough  for  technical 
purposes  by  difference  as  follows: 

Evaporate  100  c.c.  to  dryness  with  a  slight  excess  of  H2S04  in  a 
weighed  platinum  dish.  Ignite  the  residue  cautiously  till  the 
fumes  of  H2SO4  are  all  driven  off;  do  not  exceed  a  low  red  heat. 
Now  put  a  few  small  pieces  of  pure  (NH4)2CO3  into  the  dish,  and 
cautiously  heat  till  it  is  evaporated.  This  will  expel  the  acid  re- 
tained by  the  alkalies,  to  form  bisulfates.  Avoid  too  much  heat 
or  MgSO4  will  be  decomposed.  Now  cool  and  weigh  the  dish 
which  contains  the  sulfates  of  all  the  bases  in  the  original  water. 
Calculate  the  CaO  and  MgO  as  sulfates,  add  the  Fe203,  A1203 
and  SiO2,  and  deduct  the  sum  from  the  weight  of  the  sulfates  in 
the  dish.  The  difference  may  be  taken  as  sodium  sulfate. 

If  a  more  exact  determination  of  the  alkalies  is  needed,  evapo- 
rate 1  or  2  liters  of  the  water  to  dryness  in  a  platinum  dish.  Glass 
is  liable  to  give  up  alkali.  Extract  the  residue  with  water,  add  an 
excess  of  pure  milk  of  lime,  digest  and  filter,  and  proceed  with  the 
solution  as  with  the  filtrate  from  the  lime  in  the  determination  of 
alkalies  in  the  analysis  of  fire  clay.  A  blank  must  be  run  on  all 
the  reagents.  In  place  of  using  a  platinum  dish  the  water  may  be 
boiled  down  to  dryness  in  a  clean  tin  sauce  pan,  and  the  residue 
used  for  the  determination  of  the  alkalies.  This  will  be  found  a 
useful  method  where  a  number  of  waters  are  to  be  analyzed  and 
the  supply  of  platinum  ware  is  short. 

Calculation  of  the  Results. — In  stating  the  results  of  the  analysis  it 
is  customary  to  combine  the  acids  and  the  bases  in  the  following  man- 
ner: The  alkalies  are  first  combined  with  the  chlorine,  any  excess  being 
then  combined  with  the  sulfuric  acid.  Should  there  be  more  chlorine 
than  will  combine  with  the  alkalies  the  excess  is  calculated  first  to  the 
calcium  and  when  that  is  used  up,  to  the  magnesium.  Should  there  be 
alkalies  more  than  sufficient  to  saturate  both  the  chlorine  and  the  sul- 
furic acid  the  excess  is  estimated  as  carbonate. 

The  sulfuric  acid  left  after  the  alkalies  are  satisfied  is  then  united  with 
the  calcium  and  any  excess  combined  with  the  magnesium. 


314  METALLVRQ1CAL  ANALYSIS 

All  the  calcium  and  magnesium  not  required  for  the  chlorine  and  the 
sulfuric  acid  are  then  calculated  as  carbonates. 

This  order  can  be  departed  from  where  there  is  evidence  of  some  other 
combination.  In  water  that  has  been  treated  with  lime  and  soda  to 
remove  the  lime,  magnesia  is  frequently  present  as  hydroxide.  In 
estimating  the  effect  of  the  magnesia  compounds  in  causing  corrosion  in 
boilers  all  the  chlorine  and  the  sulfuric  acid  in  excess  of  that  required 
to  saturate  the  alkalies  should  be  considered  as  combined  with  the  mag- 
nesia. The  table  in  the  end  of  the  book  will  be  found  useful  in  making 
these  calculations. 

The  analysis  should  .be  reported  in  parts  per  million  and  in  grains  per 
gallon.  To  convert  parts  per  million  to  grains  per  gallon  multiply  by 
0.058353. 


CHAPTER  XXXIV 
CALCULATION  OF  NORMAL  SOLUTIONS 

A  normal  solution,  as  used  in  this  book,  is  a  solution  a  liter  of 
which  contains  1  gram  atomic  weight  of  active  hydrogen  or  its 
equivalent.  Thus  a  normal  solution  of  HC1  will  contain  1.008 
grams  of  hydrogen  or  36.468  grams  of  HC1  in  a  liter,  a  liter  of 
normal  H2SO4  will  contain  1.008  grams  of  hydrogen  or  49.043 
grams  of  H2SO4.  A  liter  of  normal  NaOH  contains  1.008  grams 
of  hydrogen  or  40.008  grams  of  NaOH,  and  a  liter  of  normal 
NH4OH  contains  1.008  grams  of  hydroxyl  hydrogen  or  35.05  grams 
of  NH4OH.  If  an  acid  such  as  H3PO4  is  used  in  a  reaction  where- 
in only  two  of  its  hydrogen  atoms  are  active  acid  ions,  a  normal 
solution  will  contain  one-half  of  the  gram  molecular  weight  of 
phosphoric  acid  in  a  liter,  while  if  in  the  reaction  all  three  of  the 
hydrogen  atoms  are  active  a  liter  of  normal  phosphoric-acid  solu- 
tion will  contain  one-third  of  the  gram  atomic  weight  of  phosphoric 
acid.  That  is,  the  amount  of  an  acid  or  alkali  contained  in  a 
liter  of  a  normal  solution  depends  upon  the  reaction  for  which  the 
reagent  is  to  be  used,  but  it  will  always  contain  1  gram  atomic 
weight  of  hydrogen  which  will  take  part  in  the  given  reaction. 

With  oxidizing  and  reducing  solutions  the  same  principle  holds 
good.  For  instance,  1  gram  molecular  weight  of  KMnO4  in  an 
acid  solution  will  give  up  oxygen  sufficient  to  oxidize  5.04  grams 
of  hydrogen;  therefore  a  normal  solution  of  permanganate  when 
it  is  to  be  used  in  an  acid  solution  will  contain  one-fifth  of  the 
gram  molecular  weight  of  KMn04  per  liter.  In  an  alkaline  solu- 
tion 1  gram  molecular  weight  of  KMnO4  will  only  oxidize  the 
equivalent  of  3.024  grams  of  hydrogen;  therefore  when  it  is  to  be 
used  in  an  alkaline  solution  (as  in  the  Volhard  method  for  man- 
ganese) a  liter  of  normal  solution  will  contain  one-third  of  the 
gram  molecular  weight  of  KMnO4. 

In  making  up  normal  solutions  (or  fractional  normal  solutions) 
of  oxidizing  or  reducing  reagents  it  is  most  convenient  to  consider 

315 


316  METALLURGICAL  ANALYSIS 

the  change  in  valence  which  the  reagent  undergoes.  Thus  when 
permanganate  is  used  to  titrate  iron  as  given  on  page  28,  the 
manganese  undergoes  a  change  of  valence  from  7  to  2,  that  is, 
a  normal  permanganate  solution  contains  one-fifth  of  its  gram 
molecular  weight  in  a  liter.  In  the  Volhard  process  the  manga- 
nese undergoes  a  change  of  valence  of  3  and  a  normal  permanga- 
nate solution  for  use  in  the  Volhard  titration  contains  one-third 
of  its  gram  molecular  weight  in  a  liter.  Similarly  when  K2Cr2O7 
is  used  to  titrate  iron  as  directed  on  page  23,  the  chromium  atoms 
undergo  a  change  of  valence  of  3  each  or  6  together.  Therefore 
a  normal  solution  of  K2Cr207  contains  one-sixth  of  the  gram 
molecular  weight  of  K2Cr2O7  in  a  liter. 

When  iron  is  titrated  with  an  oxidizing  agent  it  undergoes  a 
change  in  valence  of  one.  'Therefore  a  liter  of  a  normal  solution 
of  an  oxidizing  agent,  as  permanganate,  will  oxidize  the  gram 
atomic  weight  of  iron  or  55.84  grams  and  1  c.c.  will  oxidize  0.05584 
gram  iron  and  1  c.c.  of  a  N/10  solution  will  oxidize  (or  titrate) 
0.005584  gram  of  iron.  The  calculation  for  vanadium,  manga- 
nese, chromium,  etc.,  is  done  in  the  same  way,  remembering  that 
the  atomic  weight  of  the  element  is  divided  by  its  change  in 
valence. 

When  phosphorus  is  determined  by  the  Emmerton  process,  the 
valence  of  the  (NH4)3PO412MoO3  is  reduced  by  34;  that  is,  a 
gram  molecular  weight  of  the  " yellow  precipitate"  is  reduced  by 
the  action  of  34  grams  of  hydrogen,  and  when  it  is  oxidized  back 
by  the  standard  permanganate  enough  permanganate  must  be 
used  to  oxidize  the  same  amount  of  hydrogen  or  raise  the  valence 
of  the  reduced  "yellow  precipitate"  molecule  34.  Therefore  a 
liter  of  a  normal  permanganate  is  equal  to  the  gram  atomic  weight 
of  phosphorus  divided  by  34  and  1  c.c.  of  a  N/10  permanganate 
is  equal  to  31.04-7-34X10X1000  grams  or  0.000091294  gram 
phosphorus. 

The  use  of  normal  solutions  (or  fractional  normal  solutions) 
greatly  simplifies  calculations.  One  cubic  centimeter  of  a  normal 
acid  will  exactly  neutralize  1  c.c.  of  a  normal  alkali,  and  1  c.c. 
of  a  normal  oxidizing  solution  will  exactly  oxidize  1  c.c.  of  a 
normal  reducing  solution  (if  they  are  capable  of  reacting  with 
each  other). 


TABLES 


317 


TABLE  1.— INTERNATIONAL  ATOMIC  WEIGHTS,  1916 


Symbol 

Atomic 
weight 

Symbol 

Atomic 
weight 

Aluminium 

Al 

27  1 

Molybdenum 

Mo 

96  0 

Antimony.  . 

Sb 

120  2 

Neodymium  

Nd 

144  3 

Argon  

A  

39.88 

Neon  

Ne.  . 

20  2 

Arsenic  

As. 

74.96 

Nickel  

Ni 

58  68 

Barium  
Bismuth  

Ba  
Bi  

137.37 
208.0 

Niton  (radium  emanation)  .... 
Nitrogen  

Nt  

N  

222.4 
14  01 

Boron  

B  

11.0 

Osmium  

Os  

190  9 

Br 

79  92 

Oxygen 

o 

16  00 

Cadmium 

Cd 

112  40 

Palladium 

Pd 

106  7 

Caesium   . 

Cs. 

132  81 

Phosphorus 

p 

31  04 

Calcium    

Ca. 

40  07 

Platinum  

Pt 

195  2 

Carbon  

c  

12.005 

Potassium  

K 

39   10 

Cerium  

Ce  

140.25 

Praseodymium  

Pr. 

140  9 

Chlorine  

Cl  

35.46 

Radium  

Ra.    . 

226  0 

Chromium  

Cr  

52.0 

Rhodium  •  

Rh  

102  9 

Cobalt 

Co 

58  97 

Rubidium 

Rb 

85  45 

Columbium 

Cb 

93  5 

Ruthenium 

Ru 

101  7 

Copper 

Cu 

63  57 

Samarium  . 

Sa 

150  4 

Dysprosium   .  . 

Dy.    ... 

162.5 

Scandium  

Sc 

44  1 

Erbium           .  .  . 

Er  

167.7 

Selenium  

Se 

79  2 

Europium  

Eu  

152.0 

Silicon  

Si 

28  3 

Fluorine  

F  

19.0 

Silver  

Ag. 

107  88 

Gadolinium  .... 

Gd  

157.3 

Sodium  

Na... 

23  00 

Gallium  

Ga  

69.9 

Strontium  

Sr  

87  63 

Germanium 

Ge 

72  5 

Sulphur 

g 

32  06 

Glucinum 

Gl 

9   1 

Tantalum 

Ta 

181  5 

Gold 

Au     . 

197  2 

Tellurium 

Te 

127  5 

Helium 

He 

3.99 

Terbium  

Tb 

159  2 

Holmium     

Ho 

163  5 

Thallium       

Tl 

204  0 

Hydrogen  

H  

1.008 

Thorium  

Th 

232  4 

Indium  

In  

114.8 

Thulium  

Tm 

168  5 

Iodine  

126.92 

Tin  

Sn.... 

118.7 

Iridium  

Ir  

193.1 

Titanium  

Ti  

48.1 

Iron 

Fe 

55  84 

W 

184  0 

Krypton 

Kr 

82  92 

Uranium 

U 

238  2 

Lanthanum.   .  .  . 

La.   . 

139  0 

Vanadium 

v 

51  0 

Lead     

Pb.. 

207  .  20 

Xenon  

Xe 

130  2 

Lithium  

Li  

6.94 

Ytterbium    (Neoytterbium)  . 

Yb     . 

173  5 

Lutecium  

Lu  

175.0 

Yttrium  

Yt  

88.7 

Magnesium  

Mg  

24.32 

Zinc  

Zn  

65.37 

Mn 

54  93 

Zirconium 

Zr 

90  6 

Mercury  

Hg  

200.6 

318 


METALLURGICAL 


TABLE  2.— TABLE  OF  CHEMICAL  FACTORS 
(Calculated    from    1913    Atomic    Weights.) 


Sought 

Found 

Ag 

AgCl 

AgBr 

Agl 

Ag20 

AgC 

Al 

Al2Oi 

A1PO4 

A1208 

.A1P04 

As 

As2Ss 

As2S6 

Mg2A82O7 

Mg2P2Or 

AstO» 

As2Sa 

As2S6 

Mg2As2O7 

Mg2P2O7 

AsOj 

As2Ss 

As2Ss 

Mg2As2O7 

A9206 

As2S3 

As2S5 

Mg2As207 

B 

B2O3 

B02 

B2Oa 

BOs 

B2O3 

BiOr 

B2Oa 

Ba 

BaSO4 

BaCrO4 

BaSiFe 

BaO 

BaS04 

BaCrO4 

BaSiFe 

Bi 

Bi203 

BiAs04 

BiOCl 

Bi2Os 

Bi 

BiOCl 

Br 

Ag 

AgBr 

AgCl 

C 

C02 

C03 

COa 

Ca 

CaO 

CaCOa 

CaSO4 

CaF2 

CaO 

CaCOs 

CaSO4 

CaF2 

CaCO» 

CaO 

CaSO4 

Cd 

CdS 

CdO 

CdS04 

CdO 

CdS 

Factor 

Sought 

Found 

Factor 

0.7526 

CdS04 

0.6159 

0.5744 

CdS 

CdO 

1.1252 

0.4595- 

CdS04 

0.6930 

0.8084 

Cl 

AgCl 

0.2474 

0.5303 

Ag 

0.3287 

0.2219 

HCl 

AgCl 

0  .  2544 

0.4184 

HC1 

Ag 

0.3380 

0.6091 

ClOs 

AgCl 

0.5823 

0.4832 

KC1 

1.1194 

0.4827 

NaCl 

1.4276 

0.6734 

C1O4 

AgCl 

0.6939 

0.8041 

KC1 

1  .  3339 

0.6378 

NaCl 

1.7013 

0.6372 

CN 

AgCN 

0.1943 

0.8890 

Ag 

0.2411 

0.9992 

HCNS 

AgCNS 

0.3500 

0.7926 

CuCNS 

0.4857 

0.7919 

BaSO4 

0.2531 

0.9341 

Co 

CoS04 

0.3804 

0.7410 

CoO 

CoSO4 

0.4834 

0.7403 

Cr 

Cr203 

0.6842 

0.3143 

PbCr04 

0.1609 

1  .  2286 

BaCrO4 

0.2052 

1.6857 

K2Cr2O7 

0.3535 

1.1143 

Cr2Os 

PbCrO4 

0.2352 

0.5885 

BaCrO4 

0.3000 

0.5422 

KtCrzO? 

0.5167 

0.4912 

CrOa 

Cr2Oa 

1.3158 

0.6570 

PbCrO4 

0.3095 

0.6053 

BaCrO4 

0.3947 

0.5484 

Cu 

CuO 

0.7989 

0.8965 

Cu2S 

0.7986 

0.5994 

CuCNS 

0.5226 

0.8017 

CuSO45H2O 

0.2545 

1.1154 

CuO 

Cu2S 

0.9996 

1.1088 

Cu 

1.2517 

0.7408 

F. 

CaF2 

0.4868 

0.4256 

CaSO4 

0.2792 

0.5575 

SiFa 

CaF2 

0.6074 

0.2727 

Fe 

Fe2Oa 

0.6994 

1.3636 

(NH4)2Fe 

0.7146 

(SO4)26H2O 

0.1424 

0.4004 

FeO 

Fe2Os 

0.8998 

0  .  2943 

H 

H2O 

0.1119 

0.5133 

Hg 

HgCl 

0.8494 

0.5603 

HgS 

0.8618 

0.4118 

I 

Agl 

0.5406 

0.7182 

AgCl 

0.8855 

1.7847 

K 

KC1 

0.5244 

0.7350 

K2S04 

0.4487 

0.7780 

KC1O4 

0.2822 

0  .  8754 

K2PtCla 

0.1609 

0.5392 

KC1 

K2S04 

0.8557 

0.8888 

KCIO* 

0.5381 

TABLES 

TABLE   2.— TABLE  OF  CHEMICAL   FACTORS—  (Continued) 
(Calculated  from   1913   Atomic  Weights.) 


319 


Sought 

Found 

Factor 

Sought 

Found 

Factor 

KzPtCle 

0.3068 

P2O624MoO3 

0.0172 

K20 

KC1 

0.6317 

P206 

Mg2P207 

0.6379 

K2S04 

0.5405 

(NH4)3P04l2Mo03 

0.0378 

KC104 

0.3399 

Pb 

PbO 

0.9283 

K2PtCl« 

0.1938 

PbS 

0.8659 

Li 

Li2SO4 

0.1262 

Pb02 

0.8661 

LiCl 

0.1637 

PbSO< 

0.6831 

Li20 

Li2SO4 

0.2718 

PbCrO4 

0.6410 

LiCl 

0.3524 

PbCh 

0.8025 

Mg 

MgO 

0.6032 

PbO 

PbO2 

0.9331 

MgSO4 

0.2020 

PbSO4 

0.7359 

Mg2P207 

0.2184 

PbCrO* 

0.6905 

MgO 

MgSO4 

0.3349 

S 

BaS04 

0.1374 

Mg2P207 

0.3622 

SO2 

BaSO4 

0.2745 

MgCOa 

Mg2P2O7 

0.7572 

SO3 

BaSO4 

0.3430 

Mn 

MnS04 

0.3638 

SO4 

BaSO4 

0.4115 

MnS 

0.6314 

S04H2 

BaSO4 

0.4202 

Mn3O4 

0.7203 

H2S 

BaSO4 

0.1460 

Mn2P2O7 

0.3869 

Sb 

Sb204 

0.7897 

MnO 

MnSO4 

0.4697 

Sb2Sa 

0.7142 

MnS 

0.8153 

Sn 

SnO2 

0.7881 

Mn3O4 

0.9301 

Si 

SiOj 

0.4693 

Mn2P207 

0.4996 

Sr 

SrO 

0.8456 

Mo 

MoOs 

0.6667 

SrCOs 

0.5936 

PbMoO4 

0.2616 

SrSO4 

0.4770 

Na20  NaCl 

0.5303 

Sr(N03)2 

0.4140 

N 

NH3 

0.8225 

SrO 

SrCOs 

0.7019 

NH4C1 

0.2619 

SrSO4 

0.5641 

(NH4)2PtCl6 

0.0631 

Sr(N03)2 

0.4896 

NH3 

NH4C1 

0.3182 

Th 

ThO2 

0.8790 

(NH4)2PtCl6 

0.0767 

Ti 

Ti02 

0.6005 

Ni 

NiO 

0.7858 

U 

Us08 

0.8482 

NiCBHi4N4O4 

0.2032 

UO2 

0.8817 

NOiH 

NO 

2.0999 

U2P207 

0.7326 

NHs 

3.6995 

V 

V20» 

0.5614 

(NH4)2PtCl« 

0.2839 

W 

WOs 

0.7931 

N«Oi 

NO 

1.7997 

Zn 

ZnS 

0.6709 

NH3 

3.1707 

ZnO 

0.8034 

(NH4)2PtCl« 

0.2433 

KntPiOi 

0.4289 

P 

Mg2P207 

0.2787 

Zr 

Zr02 

9.7390 

(NH4)»P04,  12MoOa 

0.0165 

320 


METALLURGICAL  ANALYSIS 


TABLE  3.— LOGARITHMS  OF  NUMBERS 


N 

0 

i 

2 

3 

4 

5 

6 

7 

8 

9 

d 

10 

oooo 

0043 

0086 

0128 

0170 

0212 

0253 

0294 

0334 

0374 

4i 

11 
12 
13 
14 

IS 

0414 
0792 
1139 
1461 

0453 
0828 
1173 
1492 

0492 
0864 
1206 
1523 

0531 
0899 
1239 
1553 

0569 
0934 
1271 
1584 

0607 
0969 
1303 
1614 

0645 
1004 
1335 
1644 

0682 
1038 
1367 
1673 

0719 
1072 
1399 
1703 

0755 
1106 
1430 
1732 

38 
35 
32 
30 

1761 

1790 

1818 

1847 

1875 

1903 

1931 

1959 

1987 

2014 

28 

26 
25 
24 
22 
21 

16 
17 
18 
19 

2041 
2304 
2553 
2788 

2068 
2330 
2577 
2810 

2095 
2355 
2601 
2833 

2122 
2380 
2625 
2856 

2148 
2405 
2648 
2878 

2175 
2430 
2672 
2900 

2201 
2455 
2695 
2923 

2227 
2480 
2718 
2945 

2253 
2504 
2742 
2967 

2279 
2529 
2765 
2989 

20 

~~2~f~ 

22 
23 
24 

25 

3010 

3032 

3054 

307S 

3096 

3118 

3i39 

3160 

3181 

3201 

3222 
3424 
3617 
3802 

3243 
3444 
3636 
3820 

3263 
3464 
3655 
3838 

3284 
3483 
3674 
3856 

3304 
3502 
3692 
3874 

3324 
3522 
3711 

3892 

3345 
3541 
3729 
3909 

3365 
3560 
3747 
3927 

3385 
3579 
3766 
3945 

3404 
3598 
3784 
3962 

20 
19 

18 
18 

17 
16 
16 
15 
15 

3979 

3997 

4014 

4031 

4048 

4065 

4082 

4099 

4116 

4133 

26 

27 
28 
29 

30 

31 
32 
33 
34 

4150 
4314 
4472 
4624 

4166 
4330 
4487 
4639 

4183 
4346 
4502 
4654 

4200 
4362 
4518 
4669 

4216 
4378 
4533 
4683 

4232 
4393 
4548 
4698 

4249 
4409 
4564 
4713 

4265 
4425 
4579 
4728 

4281 
4440 
4594 
4742 

4298 
4456 
4609 
4757 

4771 

4786 

4800 

4814 

4829 

4843 

4857 

4871 

4886 

4900 

14 

4914 
5051 
5185 
5315 

4928 
5065 
5198 
5328 

4942 
5079 
5211 
5340 

4955 
5092 
5224 
5353 

4969 
5105 
5237 
5366 

4983 
5119 
5250 
5378 

4997 
5132 
5263 
5391 

5011 
5145 
5276 
5403 

5024 
5159 
5289 
5416 

50138 
5172 
5302 
5428 

14 
13 
13 
13 

35 

5441 

5453 

5465 

5478 

5490 

5502 

5514 

5527 

5539 

5551 

12 

36 
37 
38 
39 

5563 
5682 
5798 
5911 

5575 
5694 
5809 
5922 

5587 
5705 
5821 
5933 

5599 
5717 
5832 
5944 

5611 
5729 
5843 
5955 

5623 
5740 

5855 
5966 

5635 
5752 
5866 
5977 

5647 
5763 

5877 
5988 

5658 
5775 

5888 
5999 

5670 
5786 
5899 
6010 

12 
12 
11 
11 

40 

6021 

6031 

6042 

6053 

6064 

6075 

6085 

6096 

6107 

6117 

II 

41 
42 
43 
44 

6128 
6232 
6335 
6435 

6138 
6243 
6345 
6444 

6149 
6253 
6355 
6454 

6160 
6263 
6365 
6464 

6170 
6274 
6375 
6474 

6180 
6284 
6385 
6484 

6191 
6294 
6395 
6493 

6201 
6304 
6405 
6503 

6212 
6314 
6415 
6513 

6222 
6325 
6425 
6522 

10 
10 
10 
10 
10 

45 

6532 

6542 

6551 

6561 

6571 

6580 

6590 

6599 

6609 

6618 

46 
47 
48 
49 
So 

6628 
6721 
6812 
6902 

6637 
6730 
6821 
6911 

6646 
6739 
6830 
6920 

6656 
6749 
6839 
6928 

6665 
6758 
6848 
6937 

6675 
6767 
6857 
6946 

6684 
6776 
6866 
6955 

6693 
6785 
6875 
6964 

6702 
6794 
6884 
6972 

6712 
6803 
6893 
6981 

9 
9 
9 
9 

6990 

6998 

7007 

7016 

7024 

7033 

7042 

7050 

7059 

7067 

9 

8 
8 
8 
8 

61 
52 
53 
54 

7076 
7160 
7243 
7324 

7084 
7168 
7251 
7332 

7093 
7177 
7259 
7340 

7101 
7185 
7267 
7348 

7110 
7193 
7275 
7356 

7118 
7202 
7284 
7364 

7126 
7210 
7292 
7372 

7135 
7218 
7300 
7380 

7143 
7226 
7308 
7388 

7152 
7235 
7316 
7396 

55 

7404 

7412 

7419 

7427 

7435 

7443 

7451 

7459 

7466 

7474 

8 

N 

0 

I 

2 

3 

4 

5 

6 

7 

8 

9 

d 

TABLES 


321 


TABLE  3.— LOGARITHMS   OF   NUMBERS— (Continued) 


N 

o 

I 

2 

3 

4 

5 

6 

7 

8 

9 

d 
8 

8 
8 
7 
7 

7 

7 

7 
7 
7 

7 

_55 
56 
57 
58 
59 
60 

7404 

74" 

74i9 

7427 

7435 

7443 

7451 

7459 

7466 

7474 

7482 
7559 
7634 
7709 

7490 
7566 
7642 
7716 

7497 
7574 
7649 
7723 

7505 
7582 
7657 
7731 

7513 
7589 
7664 
7738 

7520 
7597 
7672 
7745 

7528 
7604 
7679 
7752 

7536 
7612 
7686 
7760 

7543 
7619 
7694 
7767 

7551 
7627 
7701 
7774 

7782 

7789 

7796 

7803 

7810 

7818 

7825 

7832 

7839 

7846 

61 
62 
63 
64 

7853 
7924 
7993 
8062 

7860 
7931 
8000 
8069 

7868 
7938 
8007 
8075 

7875 
7945 
8014 
8082 

7882 
7952 
8021 
8089 

7889 
7959 
8028 
8096 

7896 
7966 
8035 
8102 

7903 
7973 
8041 
8109 

7910 
7980 
8048 
8116 

7917 
7987 
8055 
8122 

65 

8129 

8136 

8142 

8149 

8156 

8162 

8169 

8176 

8182 

8189 

66 

67 
68 
69 

8195 
8261 
8325 
8388 

8202 
8267 
8331 
8395 

8209 
8274 
8338 
8401 

8215 
8280 
8344 
8407 

8222 
8287 
8351 
8414 

8228 
8293 
8357 
8420 

8235 
8299 
8363 
8426 

8241 
8306 
8370 
8432 

8248 
8312 
8376 
8439 

8254 
8319 
8382 
8445 

7 
6 
6 
6 

70 

8451 

8457 

8463 

8470 

8476 

8482 

8488 

8494 

8500 

8506 

6 

6 
6 
6 
6 

71 
72 
73 
74 

8513 
8573 
8633 
8692 

8519 
8579 
8639 
8698 

8525 
8585 
8645 
8704 

8531 
8591 
8651 
8710 

8537 
8597 
8657 
8716 

8543 
8603 
8663 
8722 

8549 
8609 
8669 
8727 

8555 
8615 
8675 
8733 

8561 
8621 
8681 
8739 

8567 
8627 
8686 
8745 

75 

8751 

8756 

8762 

8768 

8774 

8779 

8785 

8791 

8797 

8802 

6 

6 

6 
6 
5 

76 

77 
78 
79 

8808 
8865 
8921 
8976 

8814 
8871 
8927 
8982 

8820 
8876 
8932 
8987 

8825 
8882 
8938 
8993 

8831 
8887 
8943 
8998 

8837 
8893 
8949 
9004 

8842 
8899 
8954 
9009 

8848 
8904 
8960 
9015 

8854 
8910 
8965 
9020 

8859 
8915 
8971 
9025 

80 

9031 

9036 

9042 

9047 

9053 

9058 

9063 

9069 

9074 

9079 

5 

81 
82 
83 
84 

9085 
9138 
9191 
9243 

9090 
9143 
9196 
9248 

9096 
9149 
9201 
9253 

9101 
9154 
9206 
9258 

9106 
9159 
9212 
9263 

9112 
9165 
9217 
9269 

9117 
9170 
9222 
9274 

9122 
9175 
9227 
9279 

9128 
9180 
9232 
9284 

9133 
9186 
9238 
9289 

5 
5 
5 
5 

5 
5 
5 
5 
5 

85 

9294 

9299 

9304 

9309 

9315 

9320 

9325 

9330 

9335 

9340 

86 
87 
88 
89 

9345 
9395 
9445 
9494 

9350 
9400 
9450 
9499 

9355 
9405 
9455 
9504 

9360 
9410 
9460 
9509 

9365 
9415 
9465 
9513 

9370 
9420 
9469 
9518 

9375 
9425 
9474 
9523 

9380 
9430 
9479 
9528 

9385 
9435 
9484 
9533 

9390 
9440 
9489 
9538 

90 

9543 

9547 

9552 

9557 

9562 

9566 

9571 

9576 

958i 

9586 

5 

91 

92 
93 
94 

95 

9590 
9638 
9685 
9731 

9595 
9643 
9689 
9736 

9600 
9647 
9694 
9741 

9605 
9652 
9699 
9745 

9609 
9657 
9703 
9750 

9614 
9661 
9708 
9754 

9619 
9666 
9713 
9759 

9624 
9671 
9717 
9763 

9628 
9675 
9722 
9768 

9633 
9680 
9727 
9773 

5 

5 
5 
5 

5 

4 

4 
4 
4 

9777 

9782 

9786 

9791 

9795 

9800 

9805 

9809 

9814 

9818 

96 
97 
98 
99 

9823 
9868 
9912 
9956 

9827 
9872 
9917 
9961 

9832 
9877 
9921 
9965 

9836 
9881 
9926 
9969 

9841 
9886 
9930 
9974 

9845 
9890 
9934 
9978 

9850 
9894 
9939 
9983 

9854 
9899 
9943 
9987 

9859 
9903 
9948 
9991 

9863 
9908 
9952 
9996 

100 

oooo 

0004 

0009 

0013 

0017 

0022 

0026 

0030 

0035 

0039 

4 

N 

0 

I 

2 

3 

4 

5 

6 

7 

8 

9 

d 

21 


322 


METALLURGICAL  ANALYSIS 


TABLE  4.— SPECIFIC  GRAVITY  OF  HC1,  HNOi,  AND  HzSOi  AT  15°  IN  VACUO» 


Sp.  Gr. 

Per  cent,  by  weight 

Sp.  Gr. 

Per  cent,  by  weight 

HC1         HNO3          H2S04 

H2SO4 

1.000 

0.16 

0.10 

0.09 

1.570 

66.09 

1.010 

2.14 

1.90 

1.57 

1.580 

66.95 

1.020 

4.13 

3.70 

3.03 

1.590 

67.83 

1.030 

6.15 

5.50 

4.49 

1.600 

68.70 

1.040 

8.16 

7.26 

5.96  ' 

1.610 

69.56 

1.050 

10.17 

8.99 

7.37 

1.620 

70.42 

1.060 

12.19 

10.67 

8.77 

1.630 

71.27 

1.070 

14.17 

12.32 

10.19 

1.640 

72.12 

1.080 

16.15 

13.94 

11.60 

1.650 

72.96 

1.090 

18.11 

15.52 

12.99 

1.660 

73.81 

1.100 

20.01 

17.10 

14.35 

1.670 

74.66 

1.110 

21.92 

18.66 

15.71 

1.680 

75.50 

1.120 

23.82 

20.22 

17.01 

1.690 

76.38 

1.130 

25.75 

21.76 

18.31 

1.700 

77.17 

1.140 

27.66 

23.30, 

19.61 

1.710 

78.04 

.150 

29.57 

24.83 

20.91 

1.720 

78.92 

.160 

31.52 

26.35 

22.19 

.730 

79.80 

.170 

33.46 

27.87 

23.47 

.740 

80.68 

.180 

35.39 

29.37 

24.76 

.750 

81.56 

.190 

37.23 

30.87 

26.04 

.760 

82.44 

.200 

39.11 

32.34 

27.32 

.770 

83.51 

.210 

33.80 

28.58 

.780 

84.50 

1.220 

35.26 

29.84 

.790 

85.70 

1.230 

36.76 

31.11 

.800 

86.92 

1.240 

38.27 

32.28 

.810 

88.30 

.250 

39.80 

33.43 

.820 

90.05 

.260 

41.32 

34.57 

.830 

92.10 

.270 

42.85 

35.71 

.840 

95.70 

.280 

44.39 

36.87 

.841 

96.38 

.290 

45.93 

38.03 

1.8415 

97.35 

.300 

47.47 

39.19 

1.841 

98.20 

.310 

49.05 

40.35 

1.840 

98.72 

.320 

50.69 

41.50 

1.839 

99.12 

.330 

52.34 

42.66 

.340 

54.04 

43.74 

.350 

55.76 

44.82 

.360 

57.54 

45.88 

.370 

59.36 

46.94 

.380 

61.24 

48.00 

.390 

63.20 

49.06 

.400 

65.27 

50.11 

.410 

67.47 

51.15 

.420 

69.77 

52.15 

.430 

72.14 

53.11 

.440 

74.64 

54.07 

.450 

77.24 

55.03 

.460 

79.94 

55.97 

.470 

82.86 

56.90 

.480 

86.01 

57.83 

.490 

89.86 

58.74 

.500 

94.04 

59.70 

.510 

98.05 

60.65 

.520 

99.62 

61.59 

.530 

62.53 

1.540 

63.43 

1.550 

64.26 

1.560 

65.20 

JLUNGE-BEHL,  Chem.  tech.  Untersungsmethoden,  6th  edition,  Vol.  1 


TABLES 


323 


TABLE  5.— SPECIFIC  GRAVITY  OF  KOH,  NaOH,  AND  NH,  SOLUTIONS  AT  15°  C. 


Sp.  Gr. 

Per  cent. 
KOH 

Per  cent. 
NaOH 

Sp.  Gr. 

Per  cent. 
NH» 

1.007 

0.9 

0.59 

1.000 

0.00 

1.022 

2.6 

1.65 

0.996 

0.91 

1.037 

4.5 

3.22 

0.992 

1.84 

1.052 

6.4 

4.50 

0.988 

2.80 

1.067 

8.2 

5.86 

0.984 

3.80 

1.083 

10.1 

7.30 

0.980 

4.80 

1.100 

12.0 

8.78 

0.976 

5.80 

1.116 

13.8 

10.30 

0.972 

6.80 

1.134 

15.7 

11.90 

0.968 

7.82 

1.152 

17.6 

13.50 

0.964 

8.84 

1.171 

19.5 

15.15 

0.960 

9.91 

1.190 

21.4 

16.91 

0.956 

11.03 

1.210 

23.3 

18.71 

0.952 

12.17 

1.231 

25.1 

20.69 

0.948 

13.31 

1.252 

27.0 

22.50 

0.944 

14.46 

1.274 

28.9 

24.48 

0.940 

15.63 

1.297 

30.7 

26.58 

0.936 

16.82 

1.320 

32.7 

28.83 

0.932 

18.03 

1.345 

34.9 

31.20 

0.928 

19.25 

1.370 

36.9 

33.73 

0.924 

20.49 

1.397 

38.9 

36.36 

0.920 

21.75 

1.424 

40.9 

39.06 

0.916 

23.03 

1.453 

43.4 

42.02 

0.912 

24.33 

1.483 

45.8 

45.16 

0.908 

25.65 

1.514 

48.3 

48.41 

0.904 

26.98 

1.546 

50.6 

0.900 

28.33 

1.580 

53.2 

0.896 

29.69 

1.615 

55.9 

0.892 

31.05 

1.634 

57.5 

0.888 

32.50 

0.884 

34.10 

324 


METALLURGICAL  ANALYSIS 


TABLE  6.— SPECIFIC  GRAVITY  OF  ACETIC  ACID  AT  15°  C. 


Specific 
gravity 

Per  cent. 
H.CsHiOi 

Specific 
gravity 

Per  cent. 
H.CjHsO, 

Specific 
gravity 

Per  cent. 
H.CtHsOz 

Specific 
gravity 

Per  cent. 
H.C2H3O« 

0.9992 

0 

1.0363 

26 

1.0623 

51 

1.0747 

76 

1.0007 

1 

.0375 

27 

1.0631 

52 

1.0748 

77 

1.0022 

2 

.0388 

28 

.0638 

53 

.0748 

78 

1  .  0037 

3 

.0400 

29 

.0646 

54 

.0748 

79 

.0052 

4 

.0412 

30 

.0653 

55 

.0748 

80 

.0067 

5 

.0424 

31 

.0660 

56 

.0747 

81 

.0083 

6 

.0436 

32 

.0666 

57 

.0746 

82 

.0098 

7 

.0447 

33 

.0673 

58 

.0744 

83 

.0113 

8 

.0459 

34 

.0679 

59 

.0742 

84 

.0127 

9 

.0470 

35 

1.0685 

60 

.0739 

85 

.0142 

10 

.0481 

36 

1.0691 

61 

.0736 

86 

.0157 

11 

.0492 

37 

1.0697 

62 

.0731 

87 

.0171 

12 

.0502 

38 

1.0702 

63 

.0726 

88 

.0185 

13 

.0513 

39 

1  .  0707 

64 

.0720 

89 

.0200 

14 

.0523 

40 

1.0712 

65 

.0713 

90 

.0214 

15 

.0533 

41 

1.0717 

66 

1.0705 

91 

.0228 

16 

.0543 

42 

1.0721 

67 

1.0696 

92 

.0242 

17 

.0552 

43 

1.0725 

68 

1.0686 

93 

.0256 

18 

.0562 

44 

1  .  0729 

69 

1.0674 

94 

.0270 

19 

.0571 

45 

1  .  0733 

70 

1  .  0660 

95 

.0284 

20 

.0580 

46 

1.0737 

71 

1  .  0644 

96 

.0298 

21 

.0589 

47 

1.0740 

72 

1  .  0625 

97 

.0311 

22 

.0598 

48 

1  .  0742 

73 

1  .  0604 

98 

.0324 

23 

.0607 

49 

1.0744 

74 

1  .  0580 

99 

1.0337 

24 

.0615 

50 

1.0746 

75 

1  .  0553 

100 

1  .  0350 

25 



TABLES 


325 


TABLE  7.— SPECIFIC  GRAVITY  AND  PERCENTAGE  OF  ALCOHOL 

BY  VOLUME 

(Squib) 


Per  cent, 
alcohol 
by 
volume 

Specific 
gravity  at 
15.56° 

Per  cent, 
alcohol 
by 
volume 

Specific 
gravity  at 
15.56° 

Per  cent, 
alcohol 
by 
volume 

Specific 
gravity  at 
15.56° 
15.56° 

Per  cent, 
alcohol 
by 
volume 

Specific 
gravity  at 
15.56° 

15.56° 

15.56°    ' 

15.56°    ' 

1 

0.9985 

26 

0.9698 

51 

0.9323 

76 

0.8745 

2 

0.9970 

27 

0.9691 

52 

0.9303 

77 

0.8721 

3 

0.9956 

28 

0.9678 

53 

0.9283 

78 

0.8696 

4 

0.9942 

29 

0.9665 

54 

0.9262 

79 

0.8664 

5 

0.9930 

30 

0.9652 

55 

0.9242 

80 

0.8639 

6 

0.9914 

31 

0.9643 

56 

0.9221 

81 

0.8611 

7 

0.9898 

32 

0.9631 

57 

0.9200 

82 

0.8581 

8 

0.9890 

33 

0.9618 

58 

0.9178 

83 

0.8557 

9 

0.9878 

34 

0.9609 

59 

0.9160 

84 

0.8526 

10 

0.9869 

35 

0.9593 

60 

0.9135 

85 

0.8496 

11 

0.9855 

36 

0.9578 

61 

0.9113 

86 

0.8466 

12 

0:9841 

37 

0.9565 

62 

0  .  9090 

87 

0.8434 

13 

0.9828 

38 

0.9550 

63 

0.9069 

88 

0.8408 

14 

0.9821 

39 

0.9535 

64 

0.9047 

89 

0.8373 

15 

0.9815 

40 

0.9519 

65 

0.9025 

90 

0.8340 

16 

0.9802 

41 

0.9503 

66 

0.9001 

91 

0.8305 

17 

0.9789 

42 

0.9490 

67 

0.8973 

92 

0.8272 

18 

0.9778 

43 

0.9470 

68 

0  .  8949 

93 

0.8237 

19 

0.9766 

44 

0.9452 

69 

0  .  8925 

94 

0.8199 

20 

0.9760 

45 

0.9434 

70 

0.8900 

95 

0.8164 

21 

0.9753 

46 

0.9416 

71 

0.8875 

96 

0.8125 

22 

0.9741 

47 

0.9396 

72 

0.8850 

97 

0  .  8084 

23 

0.9728 

48 

0.9381 

73 

0.8825 

98 

0.8041 

24 

0.9716 

49 

0.9362 

74 

0.8799 

99 

0.7995 

25 

0.9709 

50 

0.9343 

75 

0.8769 

100 

0.7946 

TABLE  8.— REDUCTION  OF  THE  VOLUME  OF  N/10  SOLUTIONS  TO  THE  VOL- 
UME AT  20°  C.  (CORRECTIONS  GIVEN  IN  1/100  CUBIC  CENTIMETERS) 


Burette  reading 

6° 

8° 

10° 

12° 

14° 

16° 

18° 

20° 

22° 

24° 

26° 

28° 

30° 

5  cc  

0 

0 

o 

0 

0 

o 

0 

o 

o 

—  0 

—  1 

—  1 

—  1 

10  cc  

+  1 

+  !• 

+  1 

+  1 

+  1 

0 

0 

o 

o 

—  1 

—  1 

—  2 

—  2 

15  cc  

4-a 

+  fl 

+fl 

+  ?• 

+  1 

+  1 

o 

o 

o 

—  1 

—  2 

—  2 

—  3 

20  cc  
25  cc 

+  3 

+4 

+  3 
+  3 

+  3 

+  3 

+  2 
+  3 

+2 

+  2 

+  1 
+  2 

0 

-(-1 

0 

o 

-1 

—  1 

-2 
2 

-2 

q 

Q 

—  4 

-4 
—  5 

30  cc   .    . 

+  4 

+  4 

+  4 

+  3 

+  3 

+  2 

4-1 

o 

_2 

A 

—  5 

-6 

35  cc   .    ... 

+  5 

+  5 

+  4 

+4 

+  3 

+  2 

4-1 

o 

—  1 

—  3 

—  4 

-6 

-7 

40  cc  

+  6 

+  6 

+  5 

+  5 

+  3 

+  2 

4-2 

o 

—  2 

—  3 

_5 

-6 

-8 

45  cc  

4-6 

+  6 

4-5 

+  5 

+  4 

+  3 

4-2 

o 

-2 

—  4 

—  5 

—  7 

-9 

50  cc..'  

+  7 

+7 

+  6 

+  6 

+  4 

+  3 

+  2 

0 

-2 

-4 

-6 

-8 

-10 

326 


METALLURGICAL  ANALYSIS 


TABLE  9.— DENSITY  OF  WATER  AT   0°  TO  36° 

WEIGHT  IN  GRAMS  OF  1  CUBIC  CENTIMETER  OF  WATER  FREE  FROM  AIR  AT  TEMPERA- 
TURES OF  0  TO  36  CENTIGRADE  BY  THE  HTDROGEN  THERMOMETER — ACCORDING  TO 
THIESEN,  SCHEEL,  AND  DIESSELHORST  Wiss.  ABH.  D.  PHYS. — TECHN.  REICHSANAT. 

3,  68,  1900 


Degrees 

Tenths  of  Degrees 

o 

.1 

.2 

•3 

.4  I   .5 

.6 

.7 

.8  1   .9 

0 

0.999868 

874 

881 

887 

893 

899 

905 

911 

916 

922 

I 

927 

932 

936 

941 

945 

950 

954 

957 

961 

965 

2 

968 

971 

974 

977 

980 

982 

985 

987 

989 

991 

3 

992 

994 

995 

996 

997 

998 

999 

999 

*000 

*000 

4 

1  .  000000 

000 

000 

*999 

*999 

•998 

•997 

•996 

•995 

•993 

5 

0.999992 

990 

988 

986 

984 

982 

979 

977 

974 

971 

6 

986 

965 

962 

958 

954 

951 

947 

943 

938 

934 

7 

929 

925 

920 

915 

910 

904 

899 

893 

888 

882 

8 

876 

870 

864 

857 

851 

844 

837 

830 

823 

816 

9 

808 

801 

793 

785 

778 

769 

761 

753 

744 

736 

10 

727 

718 

'  709 

700 

691 

681 

672 

662 

652 

642 

ii 

632 

622 

612 

601 

591 

580 

569 

558 

547 

536 

13 

525 

513 

502 

490 

478 

466 

454 

442 

429 

417 

13 

404 

391 

379 

366 

353 

339 

326 

312 

299 

285 

14 

271 

257 

243 

229 

215 

200 

186 

171 

156 

141 

IS 

126 

111 

096 

081 

065 

050 

034 

018 

002 

*986 

16 

0.998970 

953 

937 

920 

904 

887 

870 

853 

836 

819 

17 

801 

784 

766 

749 

731 

713 

695 

677 

659 

640 

18 

622 

603 

585 

566 

547 

528 

509 

490 

471 

451 

19 

432 

412 

392 

372 

352 

332 

312 

292 

271 

251 

20 

230 

210 

189 

168 

147 

126 

105 

083 

062 

040 

21 

019 

*997 

*975 

*953 

*931 

*909 

*887 

*864 

*842 

*819 

22 

0.997797 

774 

751 

728 

705 

682 

659 

635 

612 

588 

23 

565 

541 

517 

493 

469 

445 

421 

396 

372 

347 

24 

323 

298 

273 

248 

223 

198 

173 

147 

122 

096 

25 

071 

045 

019 

*994 

•968 

•941 

*915 

*889 

•863 

*836 

26 

0.996810 

783 

756 

730 

703 

676 

648 

621 

594 

567 

27 

539 

512 

484 

456 

428 

400 

372 

344 

316 

288 

28 

259 

231 

202 

174 

145 

116 

087 

058 

029 

000 

29 

0.995971 

941 

912 

882 

853 

823 

793 

763 

733 

703 

30 

673 

643 

613 

582 

552 

521 

491 

460 

429 

398 

31 

367 

336 

305 

273 

242 

211 

179 

148 

116 

084 

32 

052 

020 

*988 

*956 

*924 

*892 

*859 

*827 

*794 

*762 

33 

0.994729 

696 

663 

630 

597 

564 

531 

498 

464 

431 

34 

398 

364 

330 

296 

263 

229 

195 

161 

126 

092 

35 

058 

023 

*989 

*954 

*920 

*885 

*850 

•815 

•780 

•745 

TABLES 


327 


TABLE    10.— HEAT    OF    COMBUSTION    OF     FUEL    GAS    CONSTITUENTS    IX 
SMALL  CALORIES  PER  GRAM-MOLECULE  (VALUE  AT  CONSTANT  PRES- 
SURE), BASED  ON  LANDOLT  AND  BORNSTEIN'S  TABLES 


Constituent 

Heat  of  com- 
bustion 

Products  of  combustion 

Carbon  (C)  (solid)         

97,000 

CO2 

Carbon  monoxide  (CO)  
Hydrogen  (H2)  
Hydrogen  (Hz) 

68,000 
58,330 
69,000 

CO* 
H20  (gas) 
H2O  (liquid) 

Methane  (CH4) 

192,160 

CO2  and  H2O  (gas) 

Methane  (CH<) 

213,500 

CO2  and  H2O  (liquid) 

Ethane  (C2H6) 

340,300 

CO2  and  H2O  (gas) 

Ethane  (C2H6)                     .             .             

372,300 

CO2  and  H2O  (liquid) 

Ethylene  (C2H4)  
Ethylene  (CzHt)          

319,760 
341,100 

CO2  and  H2O  (gas) 
CO  2  and  H2O  (liquid) 

Acetylene  (C-H2)  

301,630 

CO2  and  H2O  (gas) 

Acetylene  (C2H2)  

312,300 

CO2  and  H2O  (liquid) 

Benzene  (CeHe)  (gas) 

757,000 

CO2  and  H2O  (gas) 

Benzene  (CeHe)  (gas) 

789,000 

CO2  and  H2O  (liquid) 

Benzene  (CeHe)  (liquid) 

749,200 

CO2  and  HO  (gas) 

Benzene  (CeHe)  (liquid) 

781,200 

CO2  and  H2O  (liquid) 

Methyl  alcohol  (CHsOH)  (gas)               

158,660 

CO2  and  H2O  (gas) 

Methyl  alcohol  (CHsOH)  (gas)  
Methyl  alcohol  (CHsOH)  (liquid)  
Methyl  alcohol  (CHsOH)  (liquid)  
Ethyl  alcohol  (C2HBOH)  (gas)  
Ethyl  alcohol  (CzHsOH)  (gas)  

180,000 
149,360 
170,700 
305.400 
337,400 

CO2  and  H2O  (liquid) 
CO2  and  H2O  (gas) 
CO2  and  H2O  (liquid) 
CO2  and  H2O  (gas) 
CO2  and  H2O  (liquid) 

Ethyl  alcohol  (CzHsOH)  (liquid)  

294,700 

CO2  and  H2O  (gas) 

Ethyl  alcohol  (C2H6OH)  (liquid)  

326,700 

CO2  and  H2O  (liquid) 

TABLE  11.— TENSION  OF  WATER  VAPOR  ACCORDING  TO  REGNAULT 


Degrees 
C. 

Tension  in      !    Degrees 
millimeters      |         C. 

Tension  in 
millimeters 

Degrees 
C. 

Tension  in 
millimeters 

1 

4.940 

13 

11.162 

25 

23.550 

2 

5.302 

14 

11.908 

26 

24.988 

3 

5.687 

15 

12.699 

27 

26.505 

4 

6.097 

16 

13.536 

28 

28.101 

5 

6.534 

17 

14.421 

29 

29  .  782 

6 

0.998 

18 

15.357 

30 

31.548 

7 

7.492 

19 

16.340 

31 

33.405 

8 

8.017 

20 

17.391 

32 

35.359 

9 

8.574 

21 

18.495 

33 

37.410 

10 

9.165 

22 

19.659 

34 

39  .  565 

11 

9.792 

23 

20.888 

35 

41.827 

12 

10.457 

24 

22.184 

328 


MET  A  LL  VRGJCA  L  A  NA  L  YSIS 


TABLE  12.— VOLUME  OF  GAS  AT  0°  C.   AND   760  MM.     EQUIVALENT  TO 

1  LITER  AT  OBSERVED  TEMPERATURE  AND  PRESSURE 
Based  upon  absolute  zero=  —273.000°  C.     Ohio  State  University  School  of  Mines 


Temp.,  °C 

700 

702 

704 

706 

708 

710 

712 

714  1 

716 

718  ! 

720 

0° 

.9211 

.9237 

.9263 

.9290 

.9316 

.9342 

.9368 

.9395 

.9421 

.9447 

.9474 

2° 

.9144 

.9170 

.9186 

.9222 

.9248 

.9274 

.9300 

.9326 

.9353 

.9379 

.9405 

4° 

.9078 

.9103 

.9129 

.9155 

.9181 

.9207 

.9233 

.9259 

.9285 

.9311 

.9337 

6° 

.9013 

.9038 

.9064 

.9090 

.9116 

.9141 

.9167 

.9193 

.9219 

.9244 

.9270 

8° 

.8948 

.8974 

.8999 

.9025 

.9051 

.9076 

.9102 

.9127 

.9153 

.9179 

.9204 

10° 

.8885 

.8911 

.8938 

.8961 

.8987 

.9012 

.9038 

.9063 

.9088 

.9114 

.9139 

12° 

.8823 

.8848 

.8873 

.8898 

.8924 

.8949 

.8974 

.8999 

.9024 

.9050 

.9075 

14° 

.8761 

.8786 

.8811 

.8836 

.8861 

.8886 

.8911 

.8936 

.8962 

.8987 

.9012 

10° 

.8701 

.8725 

.8750 

.8775 

.8800 

.8825 

.8850 

.8875 

.8899 

.8924 

.8949 

18° 

.8641 

.8666 

.8691 

.8715 

.8740 

.8764 

.8789 

.8814 

.8838 

.8863 

.8888 

20° 

.8582 

.8606 

.8631 

.8655 

.8680 

.8704 

.8729 

.8753 

.8778 

.8802 

.8827 

22° 

.8524 

.8548 

.8572 

.8597 

.8621 

.8645 

.8670 

.8694 

.8718 

.8743 

.8767 

24° 

.8466 

.8491 

.8515 

.8539 

.8563 

.8587 

.8611 

.8636 

.8060 

.8684 

.8708 

26° 

.8410 

.8434 

.8458 

.8482 

.8506 

.8530 

.8554 

.8578 

.8602 

.8626 

.8650 

28° 

.8354 

.8378 

.8402 

.8425 

.8449 

.8473 

.8497 

.8521 

.8545 

.8569 

.8593 

30° 

.8299 

.8322 

.8346 

.8370 

.8393 

.8417 

.8441' 

.8465 

.8488 

.8512 

.8536 

32° 

.8244 

.8268 

.8291 

.8315 

.8338 

.8362 

.8386 

.8409 

.8433 

.8456 

.8480 

34° 

.8191 

.8214 

.8237 

.8261 

.8284 

.8308 

.8331 

.8354 

.8378 

.8401 

.8425 

36° 

.8138 

.8161 

.8184 

.8207 

.8231 

.8254 

.8277 

.8300 

.8324 

.8347 

.8370 

38° 

.8085 

.8108 

.8131 

.8154 

.8177 

.8201 

.8224 

.8247 

.8270 

.8293 

.8316 

40° 

.8034 

.8056 

.8079 

.8102 

.8125 

.8148 

.8171 

.8194 

.8217 

.8240 

.8263 

TABLES 


329 


TABLE    12.— VOLUME    OF    GAS    AT    0°C.    AND    760    MM.    EQUIVALENT    TO 
1  LITER  AT  OBSERVED  TEMPERATURE  AND  PRESSURE—  (Continued) 


Temp,  °C.          722        724 


730  ~[~~  732^734^  736~T 


0° 

.9500 

.9526 

.9553 

.9579 

.9605 

.9632 

.9658 

.9684 

.9711 

.9737 

2° 

.9431 

.9457 

.9483 

.9509 

.9535 

.9562 

.9588 

.9614 

.9640 

.9666 

4° 

.9363 

.9389 

.9415 

.9441 

.9467 

.9492 

.9518 

.9544 

.9570 

.9596 

6° 

.9296 

.9322 

.9347 

.9373 

.9399 

.9425 

.9450 

.9476 

.9502 

.9528 

8 

.9230 

.9255 

.9281 

.9306 

.9332 

.9357 

.9383 

.9409 

.9434 

.9460 

10° 

.9164 

.9190 

.9215 

.9241 

.9266 

.9291 

.9317 

.9342 

.9368 

.9393 

12° 

.9100 

.9125 

.9150 

.9176 

.9201 

.9226 

.9251 

.9277 

.9302 

.9327 

14° 

.9037 

.9062 

.9087 

.9112 

.9137 

.9162 

.9187 

.9212 

.9237 

.9262 

1(5° 

.8974 

.8999 

.9024 

.9049 

.9074 

.9098 

.9123 

.9148 

.9173 

.9198 

18° 

.8912 

.8937 

.8962 

.8987 

.9011 

.9036 

.9061 

.9085 
.9023 

.9110 

.9135 

20° 

.8852 

.8876 

.8901 

.8925 

.8950 

.8974 

.8999 

.9048 

.9072 

22° 

.8791 

.8816 

.8840 

.8865 

.8889 

.8913 

.8938 

.8962 

.8986 

.9011 

24° 

.8732 

.8757 

.8781 

.8805 

.8829 

.8853 

.8878 

.8902 

.8926 

.8950 

26° 

.8674 

.8698 

.8722 

.8746 

.8770 

.8794 

.8818 

.8842 

.8866 

.8890 

28° 

.8616 
.8559 

.8640 

.8664 

.8688 

.8712 

.8736 

.8760 

.8783 

.8807 

.8831 

30° 

.8583 

.8607 

.8631 

.8654 

.8678 

.8702 

.8725 

.8749 

.8773 

32° 

.8503 

.8527 

.8550 

.8574 

.8598 

.8621 

.8645 

.8668 

.8692 

.8715 

34° 

.8448 

.8471 

.8495 

.8518 

.8542 

.8565 

.8588 

.8612 

.8635 

.8659 

36 

.8393 

.8417 

.8440 

.8463 

.8486 

.8510 

.8533 

.8556 

.8579 

.8603 

38° 

.8339 

.8362 

.8385 

.8409 

.8432 

.8455 

.8478 

.8501 

.8524 

.8547 

.  40°      1.8286 

.8309 

.8332 

.8355 

.8378 

.8401 

.8424 

.8447 

.8470 

.8493 

330 


METALLURGICAL  ANALYSIS 


TABLE  12.—  VOLUME  OF  GAS  AT  0°C.  AND  700  MM.  EQUIVALENT  TO 
1  LITER  AT  OBSERVED  TEMPERATURE  AND  PRESSURE—  (Continued) 

Temp.,  °C. 

742  |  744 

^746 

748 

750 

752 

754 

756  |  758 

'  760 

0° 

.9763 

.9790 

.9816 

.9842 

.9868 

.9895 

.9921 

.9947 

.9974 

1.0000 

2° 

.9692 

.9718 

.9744 

.9771 

.9797 

.9823 

.9849 

.9875 

.9901 

.9927 

4° 

.9622 

.9648 

.9674 

.9700 

.9726 

.9752 

.9778 

.9804 

.9830 

.9856 

6° 

.9553 

.9579 

.9605 

.9631 

.9656 

.9682 

.9708 

.9734 

.9759 

.9785 

8° 

.9485 

.9511 

.9536 

.9562 

.9588 

.9613 

.9639 

.9664 

.9690 

.9715 

10° 

.9418 

.9444 

.9469 

.9494 

.9520 

.9545 

.9571 

.9596 

.9621 

.9647 

12° 

.9352 

.9377 

.9403 

.9428 

.9453 

.9478 

.9503 

.9529 

.9554 

.9579 

14° 

.9287 

.9312 

.9337 

.9362 

.9387 

.9412 

.9437 

.9462 

.9487 

.9512 

16° 

.9223 

.9248 

.9272 

.9297 

.9322 

.9347 

.9372 

.9397 

.9422 

.9446 

18° 

.9159 

.9184 

.9209 

.9233 

.9258 

.9283 

.9307 

.9332 

.9357 

.9381 

20° 

.9097 

.9121 

.9146 

.9170 

.9195 

.9219 

.9244 

.9268 

.9293 

.9317 

22° 

.9035 

.9059 

.9084 

.9108 

.9132 

.9157 

.9181 

.9205 

.9230 

.9254 

24° 

.8974 

.8998 

.9023 

.9047 

.9071 

.9095 

.9119 

.9144 

.9168 

.9192 

26° 

.8914 

.8938 

.8962 

.8986 

.9010 

.9034 

.9058 

.9082 

.9106 

.9130 

28° 

.8855 

.8879 

.8903 

.8927 

.8951 

.8974 

.8998 

.9022 

.9046 

.9070 

30° 

.8797 

.8820 

.8844 

.8868 

.8891 

.8915 

.8939 

.8963 

.8986 

.9010 

32° 

.8739 

.8762 

.8786 

.8810 

.8833 

.8857 

.8880 

.8904 

.8927 

.8951 

34° 

.8682 

.8705 

.8729 

.8752 

.8776 

.8799 

.8822 

.8846 

.8869 

.8893 

,  30° 

.8626 

.8649 

.8672 

.8696 

.8719 

.8742 

.8765 

.8789 

.8812 

.8835 

38° 

.8570 

.8593 

.8616 

.8640 

.8663 

.8686 

.8709 

.8732 

.8755 

.8778 

40° 

,8516 

.8538 

.8561 

.8584 

.8607 

.8630 

.8653 

8676 

.8699  1  .8722 

TABLES, 


331 


TABLE   13.— VOLUME  OF  GAS  AT  OBSERVED  TEMPERATURE  AND  PRES- 
SURE EQUIVALENT  TO  1  LITER  AT  0°  C.  AND  760  MM.  MERCURY 
Based  Upon  Absolute  Zero=  -273.000°  C.     Ohio  State  University— School  of  Mines 


Temp., 
°C. 

700 

702 

704 

706 

708 

710 

712 

714 

716 

718 

720 

0° 

1.0857 

1  .  0826 

1.0795 

1.0765 

1.0735 

1.0705 

1.0674 

1.0645 

1.0615 

1  .  0585 

1.0556 

2° 

1  .  0937 

1.0906 

1.0875 

1.0844 

1.0813 

1.0783 

1.0752 

1.0722 

1.0692 

1.0663 

1.0633 

4° 

1.1016 

1.0985 

1.0954 

1.0923 

1.0892 

1.0861 

1.0831 

1.0800 

1.0770 

1.0740 

1.0710 

6° 

1  .  1096 

1.1064 

1  .  1032 

1  .  1001 

1.0970 

1.0940 

1.0909 

1.0878 

1.0848 

1.0818 

1.0787 

8° 

1  1175 

1.1144 

1.1112 

1  .  1080 

1  .  1049 

1.1018 

1.0987 

1  .  0956 

1.0925 

1.0895 

1  0865 

10° 

1  .  1255 

1  .  1223 

1.1191 

1.1159 

1.1128 

1  .  1096 

1  .  1065 

1  .  1034 

1  .  1003 

1.0973 

1.0942 

12° 

1  .  1334 

1  .  1302 

1  .  1270 

1  .  1238 

1  .  1206 

1.1175 

1.1144 

1.1112 

1  .  1081 

1  .  1050 

1  .  1020 

14° 

1.1414 

1  .  1382 

1  .  1349 

1.1317 

1  .  1285 

1.1253 

1.1222 

1.1190 

1.1159 

1.1128 

1  .  1097 

16° 

1  .  1493 

1.1461 

1  .  1428 

1.1396 

1.1364 

1.1332 

1  .  1300 

1.1268 

1  .  1237 

1  .  1206 

1.1174 

18° 

1  .  1573 

1  .  1540 

1  .  1507 

1  .  1475 

1  .  1442 

1.1410 

1.1378 

1  .  1346 

1.1314 

1  .  1283 

1  .  1252 

20° 

1  .  1653 

1.1620 

1  .  1587 

1  .  1554 

1.1521 

1  .  1489 

1  .  1456 

1.1424 

1.1392 

1.1361 

1  .  1329 

22° 

1.1732 

1  .  1699 

1.1665 

1.1632 

1  .  1600 

1.1567 

1.1535 

1  .  1502 

1  .  1470 

1.1438 

1.1406 

24° 

1.1812 

1.1778 

1.1744 

1.1711 

1.1678 

1  .  1645 

1.1612 

1  .  1580 

1.1548 

1.1516 

1  .  1484 

26° 

1.1891 

1  .  1858 

1  .  1824 

1  .  1790 

1  .  1757 

1  .  1724 

1.1691 

1.1658 

1.1625 

1.1593 

1.1561 

28° 

1.1971 

1.1937 

1  .  1903 

1  .  1869 

1.1835 

1.1802 

1.1769 

1.1736 

1  .  1703 

1.1671 

1.1638 

30° 

1  .  2050 

1.2016 

1  .  1982 

1  .  1948 

1.1914 

1.1881 

1.1847 

1.1814 

1.1781 

1.1748 

1.1716 

32° 

1.2130 

1  .  2095 

1.2061 

1.2027 

1.1993 

1  .  1959 

1  .  1925 

1.1892 

1  .  1859 

1.1826 

1.1793 

34° 

1  .  2209 

1.2175 

1.2140 

1.2106 

1.2072 

1.2038 

1  .  2004 

1  .  1970 

1.1937 

1  .  1903 

1.1870 

36° 

1  .  2288 

1.2254 

1.2219 

1.2185 

1.2150 

1.2116 

1.2082 

1  .  2048 

1.2014 

1.1981 

1  .  1948 

38° 

1  .  2368 

1.2333 

1.2298 

1  .  2263 

1  .  2229 

1.2194 

1.2160 

1.2126 

1.2092 

1.2058 

1.2025 

40° 

1  .  2448 

1.2413 

1  .  2377 

1  .  2342 

1  .  2307 

1  .  2273 

1  .  2238 

1  .  2204 

1.2170 

1.2136 

1.2102 

332 


METALLURGICAL  ANALYSIS 


TABLE  13.—  VOLUME  OF  GAS  AT  OBSERVED  TEMPERATURE  AND  PRESSURE 
EQUIVALENT  TO  1  LITER  AT  0°  C.  AND  760  MM.  MERCURY— (Continued) 

Tornp.,  °C7  ]  722  \  724  |  726  |  728  |  730  [  732  |  734  |  736  [  738  |  740 


0° 

1.0527 

1.0497 

1.0469  1.0440 

1.0411 

1.  0383  j  1.0354 

1.0326 

1.0298 

1.0270 

2° 

1  .  0604 

1.0574 

1.0545 

1.0516 

1.0487 

1.0459 

1.0430 

1.0401 

1.0373 

1  .  0345 

4° 

1.0681 

1.0651 

1.0622 

1.0593 

1.0564 

1.0535 

1  .  0506 

1.0478 

1.0449 

1.0421 

6° 

1.0758 

1.0728 

1.0698 

1.0669 

1  .  0640 

1.0611 

1.0582 

1.0553 

1  .  0524 

1.0496 

8° 

1.0835 

1.0805 

1.0775 

1.0745 

1.0716 

1.0687 

1  .  0658 

1.0629 

1.0600 

1.0571 

10° 

1.0912 

1.0882 

1.0852 

1.0822 

1.0792 

1.0763 

1.0733 

1.0704 

1.0675 

1.0646 

12° 

1.0989 

1.0959 

1  .  0929 

1  .  0899 

1.0869 

1.0839 

1.0809 

1.0780 

1.0751 

1.0722 

14° 

1  .  1066 

1  .  1036 

1  .  1005 

1.0975 

1.0945 

1.0915 

1.0885 

1.0856 

1  .  0826 

1.0797 

16° 

1.1143 

1.1113 

1.1108 

1.1051 

1.1021 

1.0991 

1.0961 

1.0932 

1.0902 

1.0872 

18° 

1  .  1220 

1.1189 

1.1159 

1.1128 

1.1097 

1.1067 

1.1037 

1.1007 

1.0977 

1.0948 

20° 

1  .  1298 

1.1267 

1.1235 

1  .  1204 

1.1174 

1.1143 

1.1113 

1  .  1083 

1  .  1053 

1  .  1023 

22° 

1  .  1375 

1.1343 

1.1312 

1.1281 

1.1250 

1.1219 

1.1189 

1.1158 

1.1128 

1  .  1098 

24° 

1  .  1452 

1  .  1420 

1  .  1389 

1.1357 

1.1326 

1.1295 

1  .  1264 

1  .  1234 

1  .  1203 

1.1173 

26° 

1  .  1529 

1.1497 

1  .  1465 

1  .  1434 

1  .  1403 

1.1371 

1.1340 

1.1310 

1.1279 

1  .  1248 

28° 

1  .  1606 

1  .  1574 

1  .  1542 

1.1510 

1.1479 

1  .  1447 

1.1416 

1.1385 

1  .  1354 

1  .  1324 

30° 

1  .  1683 

1.1651 

1.1619 

1.1587 

1.1555 

1.1523 

1.1492 

1.1461 

1  .  1430 

1  .  1399 

32° 

1  .  1760 

1.1728 

1  .  1696 

1  .  1663 

1.1631 

1.1600 

1.1568 

1.1537 

1.1505 

1  .  1474 

34° 

1.1837 

1  .  1805 

1  .  1772 

1  .  1740 

1.1708 

1.1676 

1  .  1644 

1.1612 

1.1581 

1  .  1549 

36° 

1.1915 

1  .  1882 

1  .  1849 

1.1816 

1  .  1784 

1.1752 

1  .  1720 

1.1688 

1  .  1656 

1  .  1625 

38° 

1  .  1992 

1  .  1959 

1  .  1925 

1  .  1893 

1  .  1860 

1.1828 

1.1795 

1  .  1763 

1.1732 

1.1700 

40° 

J  .  2069 

1  .  2035 

1.2002 

1.1969 

1  .  1936 

1  .  1903 

1.1871 

1.1839 

1  .  1807 

1.1775 

TABLES 


333 


TABLE  13.— VOLUME  OF  GAS  AT  OBSERVED  TEMPERATURE  AND  PRESSURE 
EQUIVALENT  TO  1  LITER  AT  0°  C.  AND  760  MM. MERCURY— (Continued) 


Temp.,  °C. 

742  |  744  |  746 

748 

750 

752  |  754  |  756 

758  |  760 

0° 

1.0243 

1.0215 

1.0188 

1.0160 

1.0133 

1.0107 

1.0080 

1.0053 

1.0026 

1.0000 

2° 

1.0318 

1  .  0290 

1.0262 

1.0235 

1.0207 

1.0180 

1.0153 

1.0127 

1.0100 

1.0073 

4° 

1.0393 

1.0365 

1.0337 

1.0310 

1  .  0282 

1.0255 

1.0227 

1.0200 

1.0173 

1.0147 

6° 

1.0468 

1.0439 

1.0411 

1.0384 

1.0356 

1  .  0329 

1.0301 

1  .  0274 

1.0247 

1.0220 

8° 

1.0543 

1.0514 

1  .  0486 

1.0458 

1.0430 

1.0403 

1  .  0375 

1.0348 

1.0320 

1.0293 

10° 

1.0618 

1.0589 

1.0561 

1.0533 

1.0505 

1.0477 

1.0449 

1.0421 

1.0393 

1.0366 

12° 

1  .  0693 

1  .  0664 

1  .  0635 

1.0607 

1.0579 

1.0551 

1.0523 

1.0495 

1.0467 

1.0440 

14° 

1.0768 

1  .  0739 

1.0710 

1.0681 

1.0653 

1.0625 

1.0597 

1.0568 

1.0540 

1.0513 

16° 

1.0843 

1.0814 

1.0785 

1  .  0756 

1.0728 

1.0699 

1.0670 

1  .  0642 

1.0614 

1  .  0586 

18° 

1.0918 

1.0889 

1.0859 

1.0830 

1.0801 

1.0773 

1  .  0744 

1.0716 

1  .  0687 

1  .  0659 

20° 

1.0993 

1.0964 

1.0934 

1.0905 

1.0876 

1.0847 

1.0818 

1.0790 

1.0762 

1.0733 

22° 

1  .  1068 

1.1038 

1.1009 

1.0979 

1.0950 

1.0921 

1.0892 

1.0863 

1.0834 

1.0806 

24° 

1.1143 

1.1113 

1  .  1083 

1  .  1054 

1  .  1024 

1.0995 

1.0966 

1.0937 

L.0908 

1.0879 

26° 

1.1218 

1.1188 

1.1158 

1.1128 

1  .  1098 

1  .  1069 

1.1040 

1.1010 

1.0981 

1.0952 

_  28° 

1  .  1293 

1  .  1263 

1  .  1232 

1  .  1202 

1.1173 

1.1143 

1.1113 

1  .  1084 

1  .  1055 

1.1026 

30° 

1.1368 

1  .  1338 

1  .  1307 

1.1277 

1.1247 

1.1217 

1.1187 

1.1158 

1.1129 

1  .  1099 

32° 

1  .  1443 

1.1412 

1.1382 

1.1351 

1  .  1321 

1.1291  1.1261 

1.1231 

1.1201 

1.1172 

34° 

1.1518 

1.1487 

1  .  1456 

1  .  1426 

1.1395 

1  .  1365 

1.1335 

1  .  1305 

1  .  1275 

1.1245 

36° 

1  .  1593 

1  .  1562 

1.1531 

1.1500 

1  .  1470 

1  .  1440 

1.1410 

1  .  1379 

1.1349 

1.1319 

38° 

1  .  1668 

1.1637 

1  .  1606 

1  .  1575 

1.1544 

1.1513 

1  .  1483 

1.1452 

1  .  1422 

1.1392 

40° 

1.1743 

H1711  1.1680 

1.1649 

1.1618  1.1587 

1.1556 

1.1526 

1.1495 

1.1465 

334 


METALLURGICAL  ANALYSIS 
TABLE  14.— USE  OF  THE  COMMON  INDICATORS 


Substance  titrated 

Methyl  orange 

Phenolphthalein 

Other  indicators 

Acetic  acid   

Useless  

Good. 

Citric  acid 

Useless 

Good 

Useless 

Good 

Phosphoric  acid  

Good.        Changes  at 
NaHzPOi. 

End  at  Na2HPO4,   but 
indistinct. 

Cochineal  is  good 
with    change    at 
Na2HPO«. 

HC1  HNOs  H-SO4 

Good 

Good 

Good.. 

Useless 

Cochineal       and 

methyl    red    are 
good. 

Nu2C03,K2C03  

Good.        Changes  at 
2NaCl  and  2KC1. 

End    at    NaHCOs,  but 
not  sharp. 

Cochineal  is  good. 

Good 

Useless 

Cochineal  is  good. 

Sulfurous  acid 

Good.        Changes   at 

NaHSOs. 

NaOH.KOH, 

Good  

Good. 

Ba(OH)2,Ca(OH)2. 

Good       Not  affected 

Useless. 

Lacmoid  is  good. 

by  H,BO3. 

Alkali  metal  silicates  .  . 

Good.     Not  affected  by 

HUSi04. 

Cyanides  

Good. 

Good 

Methyl     red     is 

good. 

Useless       

Methyl     red     is 

good. 

MoOi.WOi  

Good.        Changes  at 

Na2MoO4,  etc. 

Is  in  general  a  good 
indicator  for  strong 
acids      and      strong 
bases      and       weak 
bases,  but  is  useless 
for       weak       acids. 
Color  is  red  in  acid 
and  yellow  in  alka- 
lies.     Must  be  used 
cold. 

Is  in  general  a  good  in- 
dicator for  strong  acids 
and  strong  bases  and 
weak  acids,  but  is  use- 
less   for    weak    bases. 
COz  must  be  absent  at 
the  end.      Color  is  red 
in  alkaline  and  color- 
less in  acid  solutions. 

Standard  solutions  used  for  titrating  are  assumed  to  be  HC1  and  NaOH. 


TABLE '8  335 

TABLE  15.— MEASURES  AND  WEIGHTS 
MEASURES  OF  CAPACITY 

A.  Dry  Measure 
1  bushel  =2150.42  cubic  inches. 

1  bushel  =  the  volume  of  77.627  pounds  of  distilled  water  at  4°  C. 
Legal:  1  liter  =0.908  quart. 

1  bushel  =4  pecks  =8  gallons  =32  quarts  =35.24229  liters. 

1  peck    =2  gallons  =  8  quarts  =  8.81057  liters. 

1  gallon    =  4  quarts  =  4.40528  liters. 

1  quart    =   1.10132  liters. 

B.  Liquid  Measure 
1  U.  S.  gallon  =231  cubic  inches. 
1  gallon  =  the  volume  of  8.3388822  pounds  =58378  troy  grains  of  distilled 

water  at  4°  C.     (Stillman,  Engineering  Chemistry.) 
1  gallon  =58318  grains  of  water  at  62°  F.     (U.  S.  Phar.) 
1  gallon  =58334.9+  grains  of  pure  water  at  60°  F.,  weighed  in  air  at  60°  F., 
at  barometric  pressure  of  30  inches  of  mercury.     (Mason, 
Examination  of  Water.) 

Legal:  1  liter  =1.0567  quart  =0.26417  gallon. 
1  gallon  =4  quarts  =8  pints  =32  gills  =3.78544    liters. 
1  quart    =2  pints  =  8  gills  =0.94636    liter. 
1  pint    =  4  gills  =0.47318    liter. 
1  gill    =0.118295  liter. 
1  cubic  foot  =  7.48  gallons  =28.315  liters  =  62.42  pounds  of  water  at  60°  F. 

(Stillman.) 

1  cubic  foot  of  water  at  62°  F.  =62.355  pounds  avoirdupois  =28320   grams. 
1  cubic  inch  of  water  at  62°  F.  =0.0361  pounds  avoirdupois  =  16.387  grams. 
(Watts'  Dictionary,  V,  1010.) 

Linear  Measure 
1  yard  =0.91440  meter. 
1  foot    =0.30480  meter. 
1  inch  =0.0254  meter. 
39.37  inches  =  1  meter. 

WEIGHTS 

1  grain  troy    =0.0648004  gram. 
1  pound  troy  =  0.822857  pounds  avoirdupois. 
1  pound  avoirdupois  =-=7000  grains  troy  =  1.215279  pounds  troy. 

Troy  Weight 

1  pound  =12  oz.  =240  pwts.  =5760  grains  =373.2418  grams. 

1  0£.  =  20  pwts.  =  480  grains  =  31.1035  grams. 

1  pwt.     =     24  grains  =     1.5552  grams. 

1  grain    =     0.0648  grams. 

1  gram  =  15.432  troy  grains. 


336  MET  ALL  URGICAL  A  N  AL  YSIS 

Avoirdupois  Weight 

1  ton=  20  hundredweight  =2240  pounds  =  1016.04  kilograms. 
1  hundredweight  =   112  pounds  =     50.80  kilograms. 
1  pound  =16  ounces  =256  drams  =7000.00  grains  =453.5900  grams. 
1  ounce    =   16  drams  =  .437.50  grains  =  28.3495  grams. 
1  dram    =     27.34  grains  =     1.7718  grams. 
1  net  ton  =2000  pounds  =29166|  ozs.  troy  =907.19  kilograms. 

Metric  Ton 
1  metric  ton  =  1000  kilograms. 

CONVERSION  OF  THERMOMETER  READINGS 

To  convert  Fahrenheit  to  Centigrade,  subtract  32  and  multiply  by  f . 
To  convert  Centigrade  to  Fahrenheit,  multiply  by  f  and  add  32. 


INDEX 


Acetate  method  for  determination 
of  manganese,  68,  70,  73, 
308 

Acetylene  in  .  gas,  279,  288,  289 
Alkalies;   determination    of   in   sili- 
cates, 299 

Alumina,  Determination  of 
in  iron  ores,  307 
in  limestones,  13 
in  silicates,  297 
in  slags,  303 
determination  of  as  phosphate, 

304 
precipitation   of   by   phenylhy- 

drazine,  309 
Aluminum,  determination  of  in  iron 

and  steel,   176 
Ammonium   persulfate   method   for 

manganese  in  steel,  89 
Annealing-evolution  method  for  sul- 
fur in  iron,  107 

Antimony,  determination  of  in  bear- 
ing metal,  233 
in    copper,    224 
in  lead,  229 

Aqueous  tension,  table  of,  327 
Arsenic,   determination  of  in  steel, 

173 

bearing  metals,  234 
copper,  224 
lead,  229 

effect  of  on  the  determination 

of  phosphorus,  42 
Arsenite    solution    for    titration    of 

manganese,  85 
Asbestos  filter,  123 
Ash,  determination  of  in  coal,  244, 

247 
Atomic  weight,  table  of,  317 


Barium,    determination    of   in    sili- 
cates,   299 
carbonate  method  for  carbon, 

117 
hydroxide,  standard  solution  of, 

292 

Bearing  metal,  analysis  of,  232 
Benzene,   determination  of  in  gas, 

279,  288 
Bismuth,  determination  of  in  copper, 

224 

in  lead,  230,  231 
Bismuthate-arsenite      method      for 

manganese,  84 
Blast  furnace  gas,  analysis  of,  264, 

275 

slags,  analysis  of,  302 
Blood  test  for  CO,  295 
Brass,  analysis  of,  240 
Bronze,  analysis,  240 
Burette   readings,    table   of   correc- 
tions for,  325 
Butylene,  determination  of,  288 

Cadmium,  determination  of  in  spel- 
ter, 237,  238 
Cain    and     Hostetter    method     for 

vanadium,  151 
Calorific  value  of  gases,  291 
CaO,  determination  of  in  limestone, 

13 

in  slag,  302 
volumetrically,  18 
free,  determination  of  in  lime- 
stone, 21 
Carbon,  determination  of  in  steel  by 

direct  combustion,  112 
in  iron  and  steel  by  solution  and 
combustion,  120 


337 


338 


INDEX 


Carbon,  determination  of  in  iron  and 

steel  by  chromic  acid,  124 
in  steel  by  color  method,  131 
in  coal,  252 
dioxide,  determination  of  in  gas, 

273,  279,  293 
monoxide,    determination  of  in 

gas,  274,  280,  295 
blood  test  for,  295 
Chemical    factors,    table     of,     318, 

319 

Chimney  gas,  analysis  of,  264,  265 
Chromate  method  for  the  determina- 
tion of  lead,  215 
Chromic  acid  method  for  carbon  in 

steel  and  iron,  124 
Chromium,     determination     of     in 

steel,  147,  149,  158,  161 
determination  of  in  steel,  colori- 

metrically,  161 
Cinchonine,     use     of    in     tungsten 

determination,  160 
Clay,  analysis  of,  295 

mineral  analysis  of,  305 
Coal,  analysis  of,  242 

coking  properties  of,  258 
effect  of  washing  on,  261 
proximate  analysis  of,  242 
ultimate  analysis  of,  252 
Cobalt,  determination  of  in  copper; 

226 

determination  of  in  steel,   139 
Coke,  determination  of  porosity  of, 

259 

oven  gas,  264,  284 
Coking  properties  of  coal,  258 
Color  method  for  the  determination 

of  carbon  in  steel,  131 
bismuth  in  lead,  224 
chromium  in  steel,  161 
manganese  in  steel,  85,  89 
titanium,  166 
Copper,  determination  of  in  bearing 

metal,  233 

in  brass  and  bronze,  241 
in  iron  and  steel,  172 
in  ores,  by  cyanide  method,  208 


Copper,  determination  of  in  ores,  by 

electrolytic  method,  203 
by  iodide  method,  199 
by  short  iodide  method,  202 
by      sulfocyanate-permanga- 

nate  method,  210 
refined,  analysis  of,  222 
Cuprous  chloride,  solution  for  deter- 
mination of  CO,  272 
Cyanide  method  for  copper  in  ores, 

208 

for  nickel  in  steel,  136 
solution,  209 

Density  of  water,  table  of,  326 

Dimethylglyoxime  method  for  the 
determination  of  nickel  in 
steel,  138 

Direct  combustion  method  for  deter- 
mination of  carbon  in  steel, 
112 

Dust  in  blast  furnace  gas,  deter- 
mination of,  284 

Electrolytic  method  for  the  deter- 
mination of  copper  in  ores, 
203,  206 

of  lead  in  ores,   213 
of  nickel  and  cobalt  in  steel,  140 

Eschka  method  for  determination  of 
sulfur  in  coal,  249 

Ethane,  determination  of  in  gas,  287 

Ether  separation  for  vanadium, 
nickel,  cobalt,  aluminum, 
etc.,  154 

Ethylene,  determination  of  in  gas, 
279,  288,  289 

Evolution  method  for  the  determina- 
tion of  sulfur  in  iron  and 
steel,  97 

Ferric    oxide,    determination    of    in 

silicates,  298 
Ferrocyanide,   standard  solution   of 

for  zinc  titration,  194 
Ferrochromium,     determination    of 

phosphorus  in,  60 


INDEX 


339 


Ferromanganese,    determination    of 

phosphorus  in,  61 
of  manganese  in,  72,  80 
Ferrosilicon,   determination   of  sili- 
con in,  66 
Ferrotitanium,      determination      of 

phosphorus  in,  60 
Ferrotungsten,      determination      of 

phosphorus  in,  61 
Ferro  vanadium,     determination     of 

phosphorus  in,  62 
of  sulfur  in,   110 
of  vanadium  in,  146,  151,  154 
Ferrous  oxide,  determination   of   in 

iron  ore,  32 

Fixed  carbon  in  coal,  244,  249 
Flue  gas,  analysis  of,  265 
Ford- Williams  process  for  manganese 

determination,  75 

Gas  analysis,  264 

sampling  of,  266 
Gases,  determination   of  in  copper, 

226 

Graphite,  determination  of  in  pig- 
iron,  133 
by  direct  weighing,  134 

Heat  of  combustion  of  gases,   table 

of,  327 
Heating  power  of  coal,  calculation  of 

from  analysis,  262 
Hempel  apparatus  for  gas  analysis, 

276 
Hesse  method  for  mine  air  analysis, 

291 

Hydrocarbon   vapor   in   gas,    deter- 
mination of,  290 

Hydrochloric  acid,  N/10,  standardi- 
zation of,  21 
Hydrogen,  determination  of  in  coal, 

252 

in  steel,  186 
in  gas,  276,  280,  282,  283,  284, 

285 

by  palladiumized  asbestos,  276 
by  CuO,  284 


llluminants,     determination    of    in 

gases,  279 

Indicators,  tables  of  uses  of,  334 
Iodine  titration  method  for  deter- 
mination of  sulfur,  79 
pentoxide     method     for     CO, 

295 

titration  method  for  determina- 
tion of  copper,  199 
of  tin,  220 

solution  for  sulfur  titration,  100 
for  arsenic,  225 
for  tin  determination,  220 
Iron,  determination  of  in  ores,  22 
in  copper,  226 
in  lead,  229 
in  spelter,  237 
in  silicates,  298 
by  K2Cr207,  22 
by  Zn  and  KMnO4,  27 
by  SnCl2  and  KMnO4,  31 

Jager- Worrell  method  for  gas  analy- 
sis, 284 

Johnson's  method  for  the  determina- 
tion of  V  and  Cr  in  steel, 
149 

Kjeldahl  method  for  the  determina- 
tion of  nitrogen  in  coal,  257 

Lead,  determination  of  in  ores,  213 
in  copper,  226 
in  spelter,  227,  228 
by  electrolytic  method,  213 
by  volumetric  chromate  method, 

215 
Lead,  refined,  analysis  of,  229 

peroxide  color  method  for  deter- 
mination of  manganese,  86 
peroxide-arsenite  method  for  de- 
termination of  manganese, 
89 
Lime,  determination  of  in  limestone, 

13,  18 

free,  determination  of,  21 
in  iron  ores,  308 


340 


INDEX 


Lime  in  slags  and  silicates,  299,  302 
volumetric  determination  of,  18 
Limestone,  analysis  of,   12 
Logarithms,  table  of,    320 

Magnesia,  determination  of,  in  lime- 
stone, 14 
determination  of,  in    iron   ores, 

308 

in  silicates  and  slags,  299,   302 
Magnesia  mixture,  40 
Manganese,  acetate  method  for  de- 
termination of,  69 
in  ores  with  low  percentage,  73 
in  ores  with   high   percentage, 

70 

in  ferro-manganese,   72 
determination    of    in    steel    by 

bismuthate  method,  84 
by  color  method,  86 
by  Ford- Williams  method,  75, 

79 
by  ammonium   persulf ate 

color  method,  89 
by  PbO2-arsenite  method,  89 
in  ores  by  Volhard's  method, 

81 

by  bismuthate  method,  86 
Manganese  dioxide,  volumetric   de- 
termination of,  77 
Mercuric  chloride  solution,  24 
Methane,  determination  of   in    gas, 
280,  283,  285,  287,  290,  294 
Methyl  orange  indicator,  57 
Microscope,  use  of  by  chemist,  vii 
Mine  air,  analysis  of,  291 
Mineral  analysis  of  clays,  305 
Moisture,  determination  of  in  coal, 

243,  245 
estimation  of,  4 
Molybdenum,    determination   of   in 

steel,  163 

qualitative  test  for,  164 
Molybdic  acid  solution,  40 

Natural  gas,  analysis  of,  264,  289 
Nessler  reagent,  179 


Nickel,  determination  of  in  copper, 

218 

in  steel,  136,  138,  141 
by  cyanide  titration,  136 
by   dimethylglyoxime   method, 

138 

and  cobalt  in  steel,  139 
Nitrogen,  determination  of  in  coal, 

257 

in  steel,  169 

Nitric  acid,  standard  solution  of,  57 
Nitroso-/3-naphthol  solution,    141 
Normal  solutions,  calculation  of,  315 

Orsat's  apparatus,  270 
Oxygen,   determination  of  in   steel, 
181 

in  gas,  274,  279 

total  in. steel,  185 

in  coal,  258 

holder,  114 

Palladiumized  asbestos,  preparation 

of,  285 
Permanent  hardness,  determination 

of,  311 

Phenolphthalein,   indicator,    57 
Phosphorus,    determination     of,    in 
carbonaceous  ores,  43 

in  coal  and  coke,  250 

in  ferrosilicon,  46,  60 

in  ferromanganese,  61 

in  ferrovanadium,  62 

in  ferrotitanium       and       ferro- 
chrome,  60 

in  ferrotungsten,  61 

in  limestone,  13 

in  mill  cinder,  43 

in  ores,  iron  and  steel,  34,  44 

in  tungsten  steel,  62 

in  vanadium  steel,  59 

by  alkali  titration  method,  55 

by  CrO2  method,  48 

by  Emmerton  dry  oxidation,  49 

by  Emmerton  wet  oxidation,  54 

by  molybdate  magnesia  method, 
44 


INDEX 


341 


Phosphorus,  by  measuring  volume 

of   the   Y.  P.,  60 
by  weighing   Mg2P2O7,   38 
by  weighing  the  yellow  precipi- 
tate, 47 
Potassium    dichromate  solution  for 

iron  titration,   23 
hydroxide     solution     for      gas 

analysis,  271 

oxide,  determination   of  in  sili- 
cates, 299 
permanganate,  solution  for  lime 

determination,    18 
for  iron  titration,  28 
for   phosphorus   determination, 

50 
pyrogallate  solution  for   gas 

analysis,  271 
Porosity  of  coke,  259 
Producer  gas,  analysis  of,  264,  275 
Proximate  analysis  of  coal,  242 

Quartering,  1 

Rectifier,  for  A.  C.  current,  205 
Reduction  of  gas  volumes,  tables  of, 

328 
Reduction  for  iron    determination, 

30 

Sampling,  1 

coals,  6 

equipment,  9 

gases,  266 

iron  ores,  7 

limestone,  12 

metals,  3 

pig-iron,  8 
Selenium,  determination  of  in  copper, 

225 
Silica,  determination  of  in  clay,  294 

in  iron  ores,  306 

in  iron  and  steel,  as  slag,  67 

in  limestone,  12 

in  slags,   303 

in  silicates,  296 
Silicates,    analysis   of,    296 


Silicon,  determination  of  in  iron  and 

steel,    63 
in  ferrosilicon,  66 
Size-weight  ratio,  2 
Sodium  hydroxide,    standard  solu- 
tion of,  56 

oxide,  determination  of  in   sili- 
cates, 299 

Solder  analysis,  241 
Specific  gravity  of  coke,  259,  260 
Specific     gravity     and     percentage 
composition  of  acetic  acid, 
table  of,  324 
of  ethyl  alcohol,  325 
of  hydrochloric  acid,  322 
of  nitric  acid,  322 
of  potassium  hydroxide,  323 
of  sodium  hydroxide,  323 
of  sulfuric  acid,  322 
of  ammonium  hydroxide,  323 
Spelter,  analysis  of,  237 

coating,    determination,    189 
Spiegel-eisen,  determination  of  man- 
ganese in,  72 
Standard  samples,  vi 
Stannous  chloride  solution,  24 
Starch  indicator,  preparation  of,  100 
preparation  of  very    sensitive, 

225 
Sulfur,   determination  of,  91 

determination  of  in  coal,  249 
in  copper,  228 
in  blast  furnace  slag,  305 
in  ferrovanadium,  110 
in  iron  and  steel,  95,  97 
in  iron  ores,  by  fusion,  93 

by  wet  oxidation,  94 
by  annealing-evolution 

method,  107 

by  Drown's  method,  107 
by    gravimetric    method,    in 

iron,  95 

by  evolution  method,  97 
by  iodine  titration  method,  99 
Sulfocyanate-permanganate  met  hod 
for  determination    of   cop- 
per, 210 


342 


INDEX 


Tar  in  gases,  264 

Tellurium,  determination  of  in  cop- 
per, 225 

Temporary  hardness  in  water,  de- 
termination of,  311 
Tension  of  water  vapor,  tables  of,  327 
Thermometer   readings,    conversion 

of,  336 

Thiosulfate    solution,    standardiza- 
tion of,  101,  201 
Tin,    determination    of    in    bearing 

metal,  233 

in  brass  and  bronze,  240 
in  ores,  219 
plate  coating,  analysis  of,    190 

determination  of,  191 
Titania,  determination  of    in  lime- 
stone, 13 
in  ores,  168 
in  silicates,  298 

effect    of    on    phosphorus    de- 
termination, 41,  42 
standard  solution  of,  169 
Titanium,  determination  of  in  steel 

by  cyanide  method,  166 
by  gravimetric  method,   167    **" 
by  color  method,   167 
by  bureau  of  standard  method, 

171 

by  precipitating  from  acid  solu- 
tion, 169 

qualitative  test  for,  in  steel,  156 
Titrating  solution,  29 
Tungsten,  determination  of  in  steel, 

158 

in  steel,  volumetrically,    161 
steel/  determination    of    phos- 
phorus in,  62 

Ultimate  analysis  of  coal,  252 


Unsaturated  hydrocarbons  in  gas, 
determination  of,  275,  279, 
288,  289 

Vanadium,  determination  of  in  steel, 

143 

in  ferro vanadium,    146,    154 
by  Cain  and  Hostetter's  method, 

151 

by  ether  separation  method,  154 
by  Johnson's  method,  149 
by  MnO2-permanganatemethod, 

143 
effect   of  on   the   determination 

of  phosphorus,  34,  59 
qualitative  test  for,  156 
Volatile  matter  in  coal,  determina- 
tion of,  243,  248 

Volhard's  process  for  the  deter- 
mination of  manganese,  81 

Waring's  method  for  the  determina- 
tion of  zinc,  196 

Washing,  effect  of  on  coal,  261 

Water,    determination    of    in    clay, 

296 

softening,  determination  of  the 
amount  of  chemicals  for, 
311 

Weighing  out,  4 

Weights  and  measures,  tables  of, 
335 

Zinc,  determination  of    in  ores   by 
ferrocyanide   method,    193 
by  Waring's  method,   196 
in  copper,   226 
in  lead,  229 

Zirconium,  effect  of  on  titanium 
determination,  171 


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